No engine "just bolts in" with the exception of a STOCK MILITARY 230 Tornado inline 6. Even the civilian engine will not. Only the 6's and at least the cummins 4bt reliably allow reuse of the STOCK radiator.
The AMC motors can be made to fit relatively easily using stock Jeep parts from the donor vehicle.
ENGINES THAT HAVE BEEN USED
inline 6 cylinders
230 military Tornado
258 AMC/Jeep
250 GM Chevrolet C41GE
292 GM
300 Ford
"V" 6 cylinders
4.3 GM
"V" 8 cylinders
305 GM
350 GM -or- Buick
366 GM
400 GM -or- Pontiac
427 GM
454 GM
455 Buick
455 Olds
502 GM
500 Caddy
360 AMC/JEEP
401 AMC/JEEP
351W Ford
460 Ford
400M Ford
318 Dodge
360 Dodge
440 Dodge
Diesel 3 cylinders
detroit 3-53 (gamma goat)
Diesel 4 cylinders
CUMMINS 4BT
HERCULES
Barreiros 4 cyl TD
Diesel 6 cylinders
6bt CUMMINS NON COMPUTER (12VALVE) to my knowledge, non intercooled
Mitsubishi 6 cylinder
Diesel 8 cylinders
6.9/7.3 FORD POWERSTROKE
6.2/6.5 GM