The only other motors that can be used are AMC specific motors: 258 I-6; 304, 360, or 401 V-8s. The auto tranny used was an AMC-cased Turbo Hydromatic 400. Finding a 258 or 360 is usually not a problem. 304-powered J trucks were pretty gutless and 401s are by far the best (and most difficult to find) motors.
73 Jeep J4000 360 .040 over, Summit K8600 Cam, Edelbrock Manifold and 750CFM 4V TH400/1339 QT
78 Cherokee Chief- Hunting Property Rig
05 Grand Cherokee- 3.7 V6 5 speed auto