I'm trying to peice together a 87 MJ with a 99 xj interior, engine harness and ax15 with a 02 4.0 out of a WJ ... What issues am I going to have?

 

Getting the 02 4.0 bolted into the XJ is going to be a problem since the motor mounts are different.

 

Pay attention! It's going into an 87 MJ. There may be more room for custom mounts. Other than that, the accessory mounts are different on the WJ engine with some mounting blots threading into the intake manifold, and the possibility of it still having the 0331 head if it's an early 02. The switchover to the "TUPY was after they ran out of 0331 existing stock. I hope you are good at electronics because there's going to be lots of changes needed.