Narrowing b-body axles

My initial plan for brakes is to do the1998-99 Jeep disc conversion outlined by Bluemissile here on the forum so my plan is to get a set of axles and cut them 28 5/16" long to accommodate additional width of the brake backing plates for that conversion. Now seeing the Dr.Diff deal above may change that but I still would like to have 4 wheel discs.
Honestly I saw a good deal ($75) for these axles and leaped before I looked.

So that leads me back to what year trucks/ vans have 8.75 rear ends?