70 440 RR with automatic trans and AC.

So I have an AVS 4640 SA, rebuilt about 10 years ago and never ran.

I also have a thermoquad 2146 just sitting on the shelf.

Since both will be a rebuild (thermoquad more extensive I believe), which is most suitable for a 440?

What intake ?
Is this a cruiser, a #s-matching car, or what ?
Either carb can be fine, stock '70 intake would need adapter for T-quad.

Factory cast iron intake. Car is heavily modified, so being correct is not the goal. I think AVS is the answer so far.

How big is that carb in CFM? I don't know if that carb # is for a 440 or 383

Application is '69 440 with A/C, which means AT as well.
I don't recall exact CFM, but I don't think it's much more than 650; (383 carbs were less, FWIW.)
I'd lean towards either a new Eddy AVS2 (650-800 CFM) for a modified street engine, better carb than the old tooling & boosters. Under $400.
Some T-quads flow 850 CFM, and the small primaries are nice at part throttle, but you'd need an adapter or a different intake.
Lots of guys prefer Holleys, too. More spendy, + fuel line, kinda more of a race carb, generally speaking.
Tuning any of the Carters seems counter-intuitive to some folks; you have to understand the metering rods, but it's simple & easy once the light comes on.

4640 is a 750cfm Carb - 440 HP

Nothing wrong with that carb especially if it’s in good shape and you want to install the flat metering rod covers , and then convert to the Edelbrock metering rods/jets

That way you can test and tune the easy way

Watch for the hot idle compensator and vacuum , I like to block them off with my own gasket

Also float level and drop is critical

And the accelerator pump leather drying out

I can’t remember what Edelbrock accelerator pump I ended up using / WAS NOT the Blue one

Flat Metering Rod Covers

Edelbrock

.101 Primary Jets - .065X.052 Metering Rods

.107 Secondary Jets makes for a good start

OE AVS's of that era 1968-mid 71 are extremely lean & as Bee said converting to the short Edelbrock performer primary jets/2 step metering rods is mandatory. & besides the jetting the "passages" may also be less than ideal for performance (I cant say as I ain't a carb guy). No knowledge of thermoquads & the tquad guru Demonsizzler in not longer in operation. Just me, you said heavily modified I would go with the new holley spread bore I forget its name (demon or avenger one of those two) & it gets multiple good reviews on here & it would require as said the adapter spacer for a square bore intake. EDIT not sure if it is spreadbore or square

That jetting combination is way to rich for my motors , especially on the secondary I would find the stock jetting and then maybe make the metering rod .002 to .005 thinner on the top step
As far as converting a AVS to use AFB parts that may be the only way you can use for tuning in today world if you don't have a Carter tuning kit for the AVS carbs
I'm lucky that I have two boxes of Carter jets and metering rods from back in the day when you could get parts form Carter at the drag races for free
OP, PM me on what your current AVS rod numbers are, I may be able to help you on getting some different ones for tuning your carb., maybe not though with out knowing what you need
I sold all my AVS carb. cores yrs ago