Car VS Truck 4-Speed Bellhousing
Yes, they might be different. Is it a V-8 or /6?
I've seen two sizes of truck/van /6 BHs, depending which size flywheel was used.
A BH from behind a 318 truck should work fine in an A-body.
V-8 (318 ) 5.125" IBR diameter BH out of an '85 Van: