EFI for my 65 Barracuda -- 2bbl or 4bbl

Yes, 4bbl. Remember that as long as the injectors are close to what you need----and the FItech/ Holley Sniper should be, they are not "cfm intensive" like a carb is. In fact you could put a 1000cfm TBI on the thing and if it's programmed/ tuned properly it would be just fine. Really the limiting factor on a throttle body is that you'd get it so huge that trying to control the throttle would be an issue, in other words "crack the barn door" and it's way too much to control

Don't discount something like buying a TBI unit of "something else" and hooking to a Megasquirt, etc Also keep in mind that if you ever expand to multiport YOU CAN STILL USE the TBI for a throttle body