A998 Trans in '66 Dart

OP,
I gotta tell you something, in case you don't know it.
The way that the TC works is that it multiplies the torque coming into it , to a higher number and sends that into the trans. This is called Torque Multiplication.
The ratio of torque in, to torque out, can be as high as 1.8 or more. The ratio is highest at zero mph, and diminishes rapidly as the car gains mph, and usually ends up at around 1.1 to 1.05, at some higher mph in top gear.
If you think about this, the TC is a completely autonomous device automatically varying it's "gear ratio" between 1.8 and 1.05, as load dictates. It's like a 2:1 transfer case but with infinitely variable inbetween ratios, and you don't have to yank the lever.

Ok so, if you compute the gear ratios to get TM numbers into the rear axles, with a wide ratio box, and include a lock-up, this is what it might look like, with 2.94 rear gears.
First gear at zero mph; ........... 2.94x2.74x1.8=14.50
same but at the top of first; ...... 2.94x2.74x1.2=9.66
Second gear; .......................... 2.94x1.54x1.2=5.46
Third gear; ............................. 2.94x1.00x1.1=3.23
Third, in loc-up; ...................... 2.94x1.00x1.0=2.94
How many actual gears is that?
Yeah, I count 5 too.

As to the torque multipliers, I did the best I could at guessing them. They could be wrong, but the point is the same, namely; that you end up with 5 working ratios; well actually 4 plus the magical autonomous TC.

As to 2.94s; I choose them, for this exercise, cuz
Firstly; 65=2375 with 27" tall tires. This is a reasonably comfortable rpm that still allows 75=2740, and I know how Americans love to open it up on their great hiways. and
Secondly; I also chose it for use in the lightweight-A cuz with a 2800TC, and any V8, this is all you need. More gear equals longer tirespin.
Thirdly; rear gears are cheap and easy to change.

I have driven this combo with a smoggerteen and a 2800TC and never lacked for power. The teener was stock except for headers and a TQ on a smallport cast iron factory intake. I admit 3.23s were a lil more fun. My combo did not have a loc-up feature, and 3.55s were the limit for me.
As to stall;
Next, by experience, I can tell you that with used 295/50-15 BFG tires, you will need about 2200 to 2500 ftlbs to the asphalt, to break them loose, and once spinning,less.
That means we can now back-calculate the crank torque required to do that.
So , I know you can't fit 295BFGs into your stock tubs, so lets go with 27" tall whatever fits, and a requirement of 2200.
2200/14.50 (with these 2.94s)=152 crank footpounds. So now all you gottado is choose a Stall-speed that will get you 152 ftlbs, and you are guaranteed to be able to break the tires loose. This does not guarantee how far they're gonna spin tho,lol.
The stall rpm will vary by engine displacement, and engine efficiency.
Generally; the bigger the engine,or the higher the efficiency; the lower the rpm can be.
As to the loc-up
But hang on, the above combo includes a loc-up feature, soooooooo, you don't "have to" select the lowest possible stall that will still spin the tires.
Now, you can bias the stall for performance somewhere else, and
#1) I like the power to be at ~32 mph .
So in the above case, with 2.94s; 32mph will be 3200rpm in first, 1800 in second. Say you are cruising along at 32mph,in second, cuz 1800 is very comfortable; but you want to increase your speed briskly, without the trans downshifting. 1800rpm will not give you much acceleration power; at least not to satisfy your requirement at this time. But if you had say a 3200TC, then your engine would be at the same power level, as if it had downshifted. She'll still be stuck with a 1.54 ratio versus 2.74, but now the torque difference at 3200 versus 1800 may satisfy the need. How sweet is that!
#2) Another time, is to overtake a slowpoke, on the hiway, who is doing say 58mph. In loc-up, you are doing 2100.Disengaging, your engine pops up to 2330, which, with a regular stall TC, will take a mile to pass that guy. If you downshift into second, the Rs pop up to ~3400, and away you go.
But if you had a 3400TC maybe your engine might have enough torque to pull off the pass in top gear, cuz instead of 2330, you are now at 3400. How sweet is that!

Of course, you might have other than 2.94 gears with different rpms; but the point is the same; with the loc-up feature, you are no longer married to a crappy stall.

And with the patterns here provided you can dial in your combo to suit your needs, with a pseudo 5-speed automatic.

BTW;
With this kindof thinking, your lightweight-A doesn't need the wide ratios. If you used a a regular 904 with loc-up, and a 2800TC, this would provide all the same benefits with the advantage of the closer ratios. The new numbers , still with 2.94s are;
A)12.97-8.64-5.11-3.23-2.94.. splits of .67-.59-.63-.91 Compare to the wide
B)14.50-9.66-5.46-3.23-2.94...splits of .67-.56-.59-.91
If you really need a deep low, then try 3.23s with a 904 at;
C)14.24-9.50-5.62-3.55-3.23 splits same as A) This would allow less stall but a higher cruise rpm. As for me, I am willing to cruise at 60=2400, And my cam sorta requires it, so this last combo is what I would run, still with the 2800TC; I love that thing.

If you're sharp, you will have noticed that the loc-up is worth one gear size or ~9% . So it will drop your cruise rpm that same 9%. This is not a fixed number.If you're cruise rpm in non-lock up is 2500rpm, then the lock-up is worth ~225rpm, if 3000, then ~270

Happy discovery Trails

EDIT; I may have mis-estimated the TM in the TC, so I'm gonna go back and do some re-calculations, to better illustrate the ratios. Not much is gonna change, but in the interest of accuracy, I'm gonna change it . And done.