My choice would be whichever had the cleanest interior, most rust free body and chassis and then source the running gear of choice from the junkyard. I wait for the local JY to have a 50% off sale (usually the day after Thanksgiving, Christmas, etc) and buy axles/transmissions for half off. Nothing better than getting a D35 and 8.8 rear for $110 OTD.
D35's are still abundant in the junkyards from 91-94 explorers, and a BOLT IN swap. The factory auto locking hubs are junk, look for warn or mile marker manual replacements online. A 95+ explorer 8.8 LSD rear with disc brakes is a very desirable swap and large braking improvement over drum brakes, but requires a little fab to make it work (spring perches need to be welded on top of the axle housing, shock tabs welded, and e-brake cable modification)
M5OD-R1 transmissions out of the explorer or 90+ ranger will be abundant as well, and bolt up to the 2.9 you have AND whatever transfer case the BII had originally whether the 1350 or 1354.
The 87 BII in my avatar had every inch of running gear rebuilt/replaced. from ball joints to u joints, Diff re-gear, and urethane pivots. that truck only had the 2.9L v6, mostly stock HP and was stone reliable.
the 87 ranger I have now, has the 8.8 rear, D35 front, M5OD 4x4 trans, 1350 manual TC. Quite the unicorn M5OD, as it is the 2.3 bell case that sits behind the 2.3 turbo engine I have. We make 310RWHP, 3.73 gears and 30x9.50x15 tires. I am stressing the M5OD quite hard, and it's taking everything I have thrown at it. The rest of the running gear has been beefed up, bigger U joints, rebuilt driveshafts, etc. so the M5OD is the weak link in my setup.
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