cutting, no (although some guys did that for reasons I don't fully understand). hammering, maybe. and if you do, it's not much. I put a TJ AX-15 into my 88 and only needed to nip of a small aluminum tab that was sticking out of the corner of the t-case. be aware that the stickshift is different too, but I'm running the TJ unit so that isn't a deal killer either. also the t-case lever action is different. I used MJ stuff and fabbed a pivot point out of a flat bar of steel. aftermarket shifters exist that don't need any of that.
you can see the little tabs on the t-case in this shot. TJ on top.
just a simple flat bar bolted to the trans