Another vote for Mercedes Benz OEM617 - that is a solid motor. I had an MB 300D for several years and regret selling it (for another Mercedes). Anyway, these engines have cast iron heads, bullet proof IP pumps that will suck glycerine from your tank (i.e. can run on WVO, used hydraulic fluid, used motor oil, biodiesel and other concoctions). I've run BioD in mine and it was super quiet.
The thing to check with this engine, however is the power curve - I believe they produce most of their torque in the upper range of the curve (around 2800-3000 rpms) - good for highway cruising but the low end grunt may suffer as a result. Again, super engines - just not sure about putting it in a crawler.
Good luck -
'95 FZJ80 with Lockers; 12,500lb winch up front. Home made sliders - and it shows...
285 DuraTracs; Seat covers, CB radio