I was looking at some upgrades for my exhaust and some small engine mods for my 1990 cherokee and everything i'm finding is for 91 4.0 I6. I'm just wondering what the differences were and if these parts would still fit or needed minor adjustments.

Any have any experiences with this or can point me in the right direction?

 

90 is still renix, so non H.O. and a closed cooling system.

91 has the H.O. and open rad/cooling design (has rad cap).

some, but not all engine parts fit. all body/drivetrain parts fit.