Brake booster

I don't know the original booster diameter.

to help me visulize your question, I tried to make a graph that shows the amount of extra force that a 7 or 8 inch booster would provide at different manifold vacuums.

at 8" of vacuum, the differance between the 7 and 8" would be about 10 pounds force at the pedal. neither one of them provides much assistance (about 40 pounds).

so going from the 8 to 7" booster, to get the same braking with 8 inHG manifold vacuum, you would have to push 10 pounds harder on the pedal. IF the manifold vacuum were to increase from 8 to 11 inHG, you would not notice the differance between the 8" to 7" booster

force at the pedal assumes 4.3:1 brake pedal ratio

That sounds negligible, which is all I wanted to know. Thanks.

I searched a little, and on Chuck M's site, it implies the booster were 8" with 9" used on the latter (didn't state what latter)

Hmm. Might be a difference in how they are measured. Without the crimp, mine measures 8" and is jammed in there against the fender. It's a very early 71. Maybe Luigi learned to move the bit over 1" after mine.