I have 2 different Buick bellhousings, one is from a smallblock 64-67 car and is Buick only with just one starter relief in it. the other is a later 68 and up BOP style and has the two starter reliefs oin it. i was looking and trying to figure out if i could use the earlier style behind a big block and i honestly cant see why you couldn't the only major differece i see is that the earlier style only has one tranny bolt pattern where the later style had the ford bolt pattern on it as well as the Muncie pattern. it looks like there would be no problem using an 11" clutch on the early style bellhousing. it looks like using an early style in a 64-67 chassis might help with header clearance also.
I once tried to put a 300 bellhousing over an 11" clutch and it didn't fit. But that was 25 years ago so my memory may be fuzzy.
