Engine Swap

Hey all, It's been a while. Got another XJ - 94' with bad motor. Question is this, has anyone had any issues with puting a 99' or 2000 4.0L motor in an earlier vehicle. Junkyards are telling me there are issues - can't see how. If it doesn't have a distributor (cam pos. sensor instead with coil packs) then I can use the distributor from the 94', Right??
Hope this is the correct spot to post this question - too many different areas to post in since i've been on here.

Thanks,
Erich