RE: different bellhousings.
Cast Iron - 55 to 57 passenger car V8, trucks used a similar design but dust covers generally don't interchange with the 55 to 57 car. Dust covers are specific to each bellhousing. Also the 55 to 57 car is not an exact replacement for the cast iron truck units as the mount pads are different. If you are not using the bellhousing as the rear mounting point this may be overlooked.
One other point is the 55 to 57 car used a 12 3/4 inch flywheel so starter installation is a problem if the engine has the 14 inch flywheel.
Aluminum ( one piece design with a small flat front dust cover ) - there are 2 basic models depending on the flywheel diameter. Easiest way to tell is the housing for the 14 inch flywheel has a curved bulge for the starter nose and the housing for the 12 3/4 inch wheel has a straight flat side at the starter location. Each of these housings requires its specific dust cover.
Even within these 2 basic styles there are variations on where the clutch fork hole is located and whether or not there are bosses for mounting a hydraulic clutch slave cylinder.
Sorry if my original reply confused you. I was trying to keep the post brief and limited to the flywhel swap onto the crank.
