Best donor car ? That's VERY VERY easy.
99' and under 5.0L 4x4 ford explorer. You get....
The best 5.0L H.o ever built ( the GT-40 headed and GT-40 intake ). Think its 245HP 305 TQ.
You get a four speed overdrive tranny.
You get a "push button" 4x4 ( advantages and disadvantages )
You get an 8.8 rear axle with disk brakes, 31 spline axles, LSD.
You get a very strong driveshaft that will fit in the jeep ( I'm pretty sure, at least the 2-door exploder version ).
And then you still get to scrap the metal truck.
My buddy almost bought one with 127K miles for $1600, and he could have driven it home. He's looking for the explorer to swap everything into his 1980 toyoda. He's swap is a bit more challenging though, since his pumkins are on the wrong side for the ford X-case. The jeep will work fine though..
Or a 4.8L v8 silverado, but that's another price range.
2002 TJ Apex edition with EFI ford 5.0L H.O., NV3550, 33'' Maxxis A/Ts, 5'' lift with custom built rear 4-link, Ford 8.8 LSD 4.10s, HP D30 with spartan locker 4.10s