As for motor mounts you will have to cut your old ones off the frame and make some new ones. I think advance adapters has some pre made motor mounts to put a AMC V8 into a YJ. Just one thing to remember about AMC V8's. The flywheels and flex plates are NOT interchangeable. They are all balanced diffrently, so if you were to bolt a flex plate from a 304 on to a 360 (or vice versa) you would be sending it to a early grave. Whatever AMC engine you choose make sure you get the right flywheel. Also the same goes for the harmonic balancers, if the engine you get happens to be missing it, make sure you get the right one.
'93 YJ 4.0L, AX-15, NP-231, SYE, CV, 8.8in rear, OME 2.5 lift, WJ knuckle/brake conversion, hydroboost. Warn M10000 winch. Hope to some day build a stroker for it.
'79 Cherokee Chief, 401 MPFI fuel injection, T-18/D-20 and hydroboost. Otherwise stock.
Future mods: NV4500, NP205, high pinion D60 front and smooth bottom D60 rear, e-lockers front & rear. SOA with 35X12.50's