How many miles? Was it well maitnenced?
Look to replace a clutch, depending on mileage.
Worn bushings.
Motor and tranny mounts.
U-joints.
T-case problems.
If it doesnt run, its kinda hard to tell whats wrong with it mechanically.
Look for the vacuum disco front, their easy to convert over to a solid shaft, but do have vacuum issues.
Depends on how much you get it for. Look it over very closely, I looked at at least a half dozen before I bought mine. Their everywhere, so dont jump on the first 'good' deal like I almost did.