Street Demon vs AVS2

With the 2.94 rear gears; 65 mph is about 2400 rpm. with a cam in your range and decent compression, pretty much any carb will do, on account of the venturies will have plenty of airflow, pushing that first-gen Charger thru the air.
I doubt if fancy boosters or small primaries will offer a significant difference. If you already had a carb in the 700 to 850 range, I would just bolt that on and go, cuz you can buy a lotta lotta gas for what a new carb will cost you. And that money would pay for any mileage difference for possibly several years. And in the mean time, you'd have a ripper of a 383.
As for the overdrive, if a GVod (.78); it could be decades before it pays for itself in fuel mileage savings alone. And I wonder if you can run it with 2.94s at 65 mph and a 220* cam. The Rs would be 1850ish, and the typical 220 cam is likely still in reversion down there.
The A500/518 overdrive ratio (.69) is even worse bringing your hiway rpm down to; 65=1640, with 2.94s; . And even the typical 210 cam with that short stroke 383, is likely pumping aircharge backwards.

But if you have to buy a carb no matter what;
Then I like your idea of a small triple-booster primary, HUGE rear dump, insulated bowl, and ...... wait;
echos of yesteryear and the 850 ThermoQuad. If you get get your cylinder pressure up closer to the detonation zone, but not into it, then that idea will be dynomite.
But the 2.94s plus overdrive idea, with a lazy-ramp 220 cam,I'm not buying it... unless 65 is not yur cruising speed. At 80mph for instance, the 2.94s with a TF-od makes about 2000 rpm in lock-up, so with a small triple-booster primary, I can see that playing nice with a fast-rate short-ramp 220 cam, but just barely.

I tell you what; I like that 220 cam, it's almost perfect for a streeter, especially a heavy first-gen Charger. What it needs is an A500 with it's 12%lower first gear equal to 12% more rear gear. And if you upgear to 3.23s, you will have a dynomite starter gear of 8.85 and still cruise at 75=2100 in loc-up, now yur talking performance, with economy.
Two things are must haves; a limited slip rear, and computerized timing, cuz to get to the mpgs at 2100, the engine will likely never get the timing it wants, to pull the big mpg numbers. I'll guess she'll like 56 or more degrees at 2100. And even if you could force 34* of all-in timing on her at 2100, and somehow keep her out of detonation,and you modded your Vcan to get another 22* out of her, now totaling 56*@2100, what happens when you floor it?
Yeah what happens with that 3.23rear?
With iron heads;
I can only tell you what has to happen, and they are all simultaneously and instantly;
The Vcan has to drop to zero-advance, to prevent detonation. This is only possible with a lot of throttle opening.
Because of that, the secondaries have to come in a lil later.
The loc-up has to kick out, to prepare for;
The trans has to kick down to a gear that provides at least 3600rpm., to deal with that 34* all-in timing.
The carb has to get fresh cold air and she has to go slightly rich, so the plugs can cool off in a hurry, cuz running lean, they will be hot. If you run a cooler plug, they will likely foul around town.
With iron heads, a stand-alone timing computer is pretty much mandatory for getting the big-number mpgs, so you can better set and control; the power-timing, the idle-timing the PartThrottle timing and the cruise-timing.
Course if your compression ratio is down in the basement, then some of these problems go away. But low-compression and big-number mpgs with a 220 cam should never be said in the same breath.
Ok but that 383, at 3600 rpm, at WOT, and 80% VE is calling for 320 cfm. Which is likely more than the 650 Demon can pass on those reduced size primaries. But recall that the secondaries have to be delayed until all those other things have taken place, which are required to keep your engine out of detonation.
So here's a situation;
You are bombing down the hiway at 75=2100, and you encounter a slow poke who because of traffic, slows you down to 65 say. So now you are at 1820 still in lock up, and you're looking for a hole to get around him, and when it appears, you floor it.
Ok so, the Vcan drops her load, the timing drops to 32*, and the carb is desperate to open the secondaries. But at 2100 she has to wait, you made it so. Next the loc-up drops out and the Rs climb to 2200, next the trans hunts for second gear, finds it ,downshifts into second and the Rs climb to 4200@65mph, and still at 32* timing. Now yur set for the secondaries to open, and good thing cuz at 4200 your engine, now at maybe 85% VE is asking for 400cfm. And don't shift her until back at 75 mph now at 4900 in second, where she might be calling for 520cfm at say 95% VE.
That's how it has to work, with factory timing controls, when biased for fuel economy.
But recall that I guessed at the 56* of cruise timing. What if your chambers want more? Less will be easy, but more ; not easy at all. Maybe impossible. But be of good cheer, those last 4 degrees hardly amount to spit difference in terms of mpg. They are bragging rights, for when you come on FABO, and present a number so high that everyone will immediately pounce on you, saying it's impossible. When that happens, my response is this;"Just cuz you can't get this number, doesn't automatically make it impossible".

With aluminum heads it's a different story. A better story, way better . But you have to consider the whole combo, and optimize it. You can't just throw it together and hope for the best.
Well,, with a 360, it actually does pretty much fall together, partly because of the 3.58 stroke. It's just a very flexible combination. Not dissing your 383 not by any means, just saying.
Now I know the A500 doesn't bolt onto your BB, but I used the 2.74/1.54/1.00 numbers anyway, cuz the 3.23s really like that trans. The A518 will only slow your take-off a lil bit, on account of the starter gear is 11.8% less effective, so you just press a lil harder on the gas-pedal,lol. I mean after all, it is a 383,lol.

Yeah so, just trying to help;
Happy HotRodding