Bellhousing Compatability

I was not aware that any small block cars came with 11" clutches. I would venture it is the same set up as the 9.5" and 10" clutches used in slant 6's, the 10" was a heavy duty fleet application. Both sizes bolted to the same flywheel and were used with the same bell housing.

I think you are over thinking the whole casting number thing. If it's a A833 4spd (can't bolt a 4spd to some of the 3spd bell housings) small block bell housing with the 5.125" bearing retainer hole it will work. The brackets the fork pivots on only vary in that they bolt down differently to accommodate the size of the bearing retainer hole (the later truck/van bell housings use a ball pivot for the fork but they work just fine in an A-body, I did it). Also, the later bell housings have the holes that the z-bar pivot bolts to moved slightly so you will need the pivot for the same generation bell housing).