Gearing ?

I reread the thread, and specifically, I reread post #1.
I think you have some good ideas.

But I 'll counter your good ideas with one of my one.
First is this; I think you said your P/W as 10.0.
This translates to about 107 in the qtr.
I think that early-Barracuda is several hundred pounds lighter than the next generation. I think it quite a bit lighter than a 70Swinger 340, which mine scaled at 3330 me in it@ 130 back in 71,lol;, so that's a net of 3200 on the Dart. I'm guessing yours will come in under 3000 plus your weight with gear, rounds to 3200 maximum..
So that means no problem building the teener to hit the target 320hp.
So lets say the target P/W of 10/1 is done.
But you wanted to hit it with up to 100hp N20, for a total of 420hp. Now, that then makes a P/W of 7.6 and the new mph to go with that is 118. This is no longer a 2 gear project.
So lets back up the bus.
The optimum gear for 118 depends on your engines power peak. I'm gonna guess that with a 220ish cam, you're gonna have a hard time making 320hp.(BTW, I'm not keen on that Voodoo). But let's say you do get the combo up to 320 no matter what. Lets say the cam you finally install makes peak power at 5600.
But lets back up some more.
You have an A999 with the ratios of 2.74-1.54-1.00, and splits of 56.2% and 64.9%. These numbers are pretty wide. You are not gonna cover that with a 110*cam. Ima thinking the 1-2 shift needs more than 114, while the 2-3 might be ok with 114*. Using a cam with this wide an LSA, means the absolute power number will be down some, while the average will be up. But to make the most with that tranny, a 110 will cost you.
Ok back to the 5600peak. I'm betting this is gonna be a 232* or bigger cam.And if you get a fast rate, that will be about a 274. This is streetable in a 367,lol. In a teener, maybe it's getting up there, so I understand your Rhoads idea. (but if you are serious about those, I would run a bigger cam and make it worth the expense). So Lets say that 5600 is doable, and the ported heads stretch the top end out to 6300.
This is where it all falls apart.
Shifting at 6300 drops the Rs into second at 3540. With a 5600rpm power peak, the torque peak comes in around 4200. You see whats happening here, right. The little teener is gonna have to claw it's way outta that hole to get back to where the power is. Not only is she way below the power-peak, but she is also quite far below the torque-peak. That tranny is costing you roughly 190 rpm on the 1-2 shift, as compared to a 904. With the tighter A904 gear spacing the drop from the same 6300, would be to 3730. With the shorter powerband requirement, of the A904, you could also reduce the LSA and pick up some peak power, giving up some, where it's not needed. BUT, lets carry on with the A999. On the 2-3 shift, the Rs will drop from 6300 to 4345. This makes the powerband requirement now only 1955. And the 114* cam is now costing you mph.
Recap
The 114* and the A999 is a bad combo, for dragracing.

But lets continue.
So we want to hit 118, having pulled every bit of power out of the teener before the power plummets. So, lets say with your ported heads, the power extends 500 past the peak of 5600, so 6100. A little math says you need 3.73s with 5% slip and 25.5 tire. Wow, that's not so bad. These will get you 3200@65mph with 0 slip. The starter gear will be 12 /( 25/2x2.74x3.73)=9.81, hey that's pretty good too.
Now let's see what it does NA. Same 320 hp/A999.Same 107 target with the 10/1 P/W, now with 3.73s . I get 5532 with 5% slip in direct.Hey it could be worse!
So that's one plan using your 320hp engine and the A999

I have another plan. I hope a better one.
First my thinking;
I think a 320 hp teener is pretty pipey, with a 274 cam.I've never had Rhoads cuz I have more engine, but they ain't cheap.My idea is to make the engine fit your 2plus 1 idea.I think it's a good one. If you build the engine for torque, it will be way more fun around town and pull harder during an Autocross event, which are run mostly in one gear.Then you can juice it up and run whatever mph you want until it blows up. So how would we do that?
Well lets pick a gear first.
Since you would like to keep the 25s, lets go with 2.94s. This gets you 65@2550 w/zero slip.
So then lets take some power out of that teener.How much. Well lets say we target 6000@the top of second, with those 2.94s,and she is well past her prime.This makes 96mph with 5% slip. in a 3200 pound car, this is a P/W of about 13.8, so we need just 232 hp. That is the minimum to go 96mph.
Now back up a sec. The reason we only went 96 is cause we ran out of rpm.And part of that was the 1.54 second gear. The A904 second would get you 101.5mph, which requires a P/W then, of 11.6, or 276hp. Now let that digest. It took 276 less 232 =44 hp to go from 96 to 101.5!
The stock teener was advertised at 230hp. You slap a 4bbl and headers on it and that can jump to 250 pretty easy. Add a little compression, and just a bowl clean up and you are at 275 and more pretty easy. and no big cam. That stock 240/114 cam, is not gonna pull to 6000 tho.
So lets compromise. We'll put just a little cam into it and sub in 2.76s, and target 100mph. This will require a p/w of 12.3, and that is 260hp. Easy-peasy.
And it will require 5900 rpm with 5% slip,to hit 101.5.
Ok,now we are getting somewhere. We need 260 hp and 5900 thru the traps.
Now since this is a streeter, and you are gonna supercharge it,the engine will not necessarily have to be pulling that hard at 5900, it just has to go there.
So,lets pick a cam that doesn't require the Rhoads,nor a rollercam. Lets go with a 260Advertised/216ish@050 This is a great torque cam and you can tune it for great fuel-economy.
So this cam will peak around 5000 in a teener.And it will torque peak at about 3750.With the right valve springs it will hit 5900 easily.
So to recap
We have at least 260 hp(probably closer to 275 or even better) that peaks around 5000, and pulls to at least 5900. It goes 100mph in the qtr at the top of second, with 2.76s. It cruises at 65=2368 with zero slip.The starter gear is 12/(25/2x2.76x2.74)=6.72. The extra torque of the smaller 260cam will get you off the line quicker than the 274cam. The stock TC will be just fine, allbeit I would go with at least a 2400, on account of that steep starter gear.2800 would be better.
Now here's the good part;Peak torque at 3750 is 36 mph in first gear. Think about that. Think about cruising along at 35 mph,in Drive, just loafing along at 1300rpm, and then the urge hits. You slam the pedal down, the tranny kicks down two gears,the secondaries open,and Shazzam!, the teener is frying the tires! Now imagine autocrossing,and having peak torque or near-peak torque,available almost all the time.
But let's go racing! Ima thinking that teener is gonna be making more than 260hp with that 260 cam. I think it will be an easy 275. And you will want to max out those 2.76s now. So lets go back to the powerpeak at 5000. If you clean up the heads, they will still be strong at 5600. So lets max her out a 5600. I get 146 mph. Well that is about 800hp, so I guess we can't max her out after all. Ok that just means we have enough gear to go there, even if we can't actually go there,lol.
Ok then, we know the SBM will easily go to 450 hp so this would be 450less 275= a 175 shot. You were planning a 100, so lets compromise and now go with a 150shot. This will get us about 425 hp and a P/W of 7.53. And that should go about 118mph and that would be about 4500.Well at 4500 she may not be cranking out 425 hp yet on the 150 shot. If you wanna go 118 you might need a lil more. Or maybe 118 is fast enough.
I tell you what; I would be scared to go 118 on those skinny rollers,lol.
So that's my idea. Give up a little motor for a funner time.
Also, special note, if you build this right, it will burn skunk-pee,day in and day out.With iron heads, this is a Dcr of between 8/1 and 8.5/1, plus tight-Q.You will save thousands of dollars over the next ten years,the life of the engine.
Also, you can build more hp,but invariably that will raise your power peak, and increase the need for a bigger TC. It will burn more gas just cruising around.
Also with a power peak around 5000, you can keep the teener heads. I wouldn't even bother fitting big valves. With 2.76s first gear is good to over 50 mph So you won't be needing them for city driving. I can see them being beneficial as the speed goes up; say over 75mph (4500 in second); and also for autocrossing. But 2.02s would be overkill I think.
Anyhow, I tried to marry your excellent thinking, with some of my ideas and experiences. See how it fits.