Use the 2wd MJ parts to get the 4wd MJ running. Sounds like a great deal regardless.
If you want to do limited wheelin with the 2wd MJ, at least put a limited slip in the rear axle.
I picked up an 88 MJ 4.0L 4x4 shortbed a few weeks ago for $150 US, and it runs. Straight body. It's gonna be one heck of a wheelin jeep, when I get some time.