Will 4.0 from 2001 Cherokee interchange with Jeep -CJ5 4.2 1981?

 

I assume you want to drop a 4.0 in the CJ? The bellhousing-engine bolt pattern is the same. If you're moving over the fuel injection as well, you'll need the 4.0l bellhousing and transmission in order to mount the crank position sensor. I don't have any info on flywheel, etc if you start mix-matching transmissions. Later transmissions might be longer and you'll run into rear drive shaft length issues. I dunno if motor mounts will work, likely need to weld up something custom.