It all comes down to tuning the carb for the engine/car combo. The AVS2 650 is certainly not too big for the 318 since the factory put thermoquads on those smogged up engines in the 70's.
I agree. The secondary air door on the AVS can be pretty much shut down making the carburetor a two barrel. They're even tuneable on a 273, of course with appropriate metering rod and jet changes. They're usually pretty close there as it is.