8 3/4" from a 1/2 Ton P/U or Van For "A" Body

Measure the bolt pattern to make sure but I believe they were all 5 on 4-1/2".

There were a few 1/2 ton 4x4s made from 72-74 with a FIVE inch BP 8 3/4 housing. It's a bolt in swap for the 85-92 trucks if you want an 8 3/4. Other than that the 8 3/4 truck housings were 4 1/2 BP. Also note that trucks had the spring pads UNDER the leaf springs rather than on top of them, so they have to be relocated. The A-100 trucks and vans had the most narrow rears. The easiest non-a body 83/4 swap is still the 66-70 B body rear. here's a Mopar Muscle article on that:
http://www.moparmusclemagazine.com/...404_8_3_4_rear_axle_housing_swap/viewall.html