rear disc from grand cherokee on a 8 3/4

Michael,
there are two problems with the swap that need to be overcome.
First is that the stock length axles are 5/16" too short, this is the space taken up by the cherokee backing plate. by using the plate, there is that much less contact at the diff of the splined end of the axle.
Second moving everything out brings the bearing out of the end of the axle tube that much. Using the spacer (cut down race) and having your machine shop set the bearing 5/16" back from its normal position solves these problems.
I have not yet assembled everything, still waiting for 4 link parts before assembly.
Andrew