The vac disco is mostly moot. I prefer not to have it, but it doesn't matter.
Later axles are better in that the wear parts are more plentiful and cost less. But it doesn't matter that much. Regardless of what you pick up, it will likely need new bearings, seals, etc, so you will be in it for a bit.
If I was you I'd look for a later HPD30 and 29 spline Chrysler 8.25. Plenty strong for what you're doing, and if they're from the same donor it's easy to remember what you need to ask for when buying wear parts.