If you use my kit with the 86-91 axle, the spring hangers will be the only part that works. Everything else is made to work with the 99-04, so there will be some part hunting involved. Just for an example, the drag link adjuster will be too short. I have these machined to the proper length for my conversions since the van frame is wider than the trucks that the steering is made for. Little things like this may or may not be a headache to you.
I understand the strength of a kingpin axle, but there's nothing wrong with a ball joint for these van applications. The ball joints & unit bearings last well over 100K, and failures are pretty uncommon.
The 14 bolt can't be used in the van because of the rear axle VSS sensor... (had one in my 78 van)
You nailed the divorced t-case problem, not enough room. The fuel tank needs to be shortened for every van conversion (my kit looses 3 gallons) so there simply isn't enough room for a divorced case.
Hope this info helps you plan the build, let me know if you have any other questions!