The two biggest problems will be :
Gear ratio. The I-6 has a different gear ratio than the the V-8.
Wheel bolt pattern. The ZJ uses a 5 bolt on 4.5" pattern. The WJ uses a 5 bolt on 5" pattern. So if you just plain did an axle swap, you'd have to do both axles or you'd have different wheels on the front and back.
And as said above, the ZJ uses two lower and two upper control arms. The WJ uses two lower control arms, but it has a center mounted "A" arm on the top.
1997 ZJ 5.2 Orvis, Baby!
1953 Willys M100 trailer Tagalong