If you really want a diesel, think about a 6.2 from a Chevy/GMC. People say they are crap, I had one for 2 years in a 3/4 ton and it had plenty of power for it, it would proabbly make an XJ move pretty good. Same motor mounts as a SBC. Cooling may be the only issue though. Much cheaper than buying a 4bt. I just sold the truck this week, if I had the space, I would have loved to have put the drivetrain in my '73 CJ-6, it would be different, that's for sure.