clutch size

Depends on "what flywheel"

EXample:

My 69 383 RR used a "real" 11" clutch with a "real" 11" bolt pattern

My 70 had a more compact bell, and used a "fake" 11" clutch which actually uses a 10.5" bolt pattern. That clutch was a constant PITA. The disc was so close to the pressure plate mounting ears that it would "fuzz up" with use and drag, preventing a clean release.

Nowadays many folks call these a 10.9" or 10 7/8" inch, but the factory called them 11" when they were new.

GM did the same horrid thing with pickups. Friend of mine had a new 70 Chev 4x4 with a scalloped clutch, and had trouble with it

Are you working with a big or small block, as you didn't say? I was not aware that any of the small block passenger cars ever used anything larger than 10.5?