71 carbs are not the way to go, hard to find, and backwards from 72 and up. 72 to 74 or 75 where the best because of the fuel inlet pos. and not all the add on emmision crap. the trap door is the secret to making these work right. there where to types, get the larger front barrels,440 cars, jury rig a choke and keep working with the rods and plunger springs, depends on the vacuum at idle,i.e. cam, good luck