found a 1990 4.2l stroker straight 6 xj with 151k whole jeep should i buy that and put the internals into the 84? The guy will sell me the 1990 xj for cheap to

 

You can but you will have to make a slight modification to the firewall. All you have to do is indent it a little with a small sledge. I'll send you a link tomorrow to a buddy's build where he did the 2.5L/2.8L to 4.0L swap (A 4.2L and 4.0L are the same size/dimensions externally) so you can see what all needs to be done.

 

So i'm getting the motor and main wiring harness is their anything else i should get from the guy he's parting it out??

 

does anyone have a site for the straight 6 bolt on to the frame engine mounts?

 

just about anywhere you want. Oreillys, autozone, brown dog, m.o.r.e., and dozens more.