Well, theory aside, I got my carb and installed it today, here is my feedback! The Holley 2300 fit exactly in place of my Autolite 2100, Holley even provides a new base gasket. I had to mess with the fuel line, went to NAPA and got a 90 degree 3/8 fitting to attach new fuel line and an inline filter to. Strange Holley doesnt supply a fuel line connection. The linkage hookup required fabbing up a new retaining clip for the throttle rod, the old one wouldnt fit and the Holley one didnt work either. I noticed my pedal wouldnt open up the carb all the way, found my old pedal linkage had been tromped on so many years the pedal needed to be bent up from the floor a bit. I left the choke wide open and didnt add a choke cable, being in Myrtle Beach SC I dont have warm up problems anyway. The car fired up and idled pretty well right off the bat. I installed a new Holley chrome air cleaner and a vented oil fill cap and took it for a spin, and found at least 30 horsepower has been added. Throttle response is crisp, no bogging at all. It burns rubber from a dead stop, chirps the tire going into second (C4 trans) and has strong punch stomping on it at 60. I ran it up to 100 and it pulled strong all the way. Huge improvement over the old Autolite, and the carb, air cleaner and oil cap cost 280 bucks from Jegs. I dont think id get that much more from a 4 bbl carb in this tune so I am real happy with this set up. Thanks to D Hearne for his advice and everybody else here too.
Glad to see someone else learn first hand from what I've experienced. Yea, I agree with the others that a 4 bbl will get you this and mileage too, but if you drive sensibly you can also get mileage from the 500 as well. The part that affects it most here is that 50 cc accellerator pump. 
