273 engine swap into a Jeep CJ5

What transmission is in there now, T-176 4-speed? The easiest path forward if you must put a 273 in it would be to use an AX-15 5-speed out of a 318 Dakota which will almost bolt to the Dana 300 transfer case, or a NP435 out of a Dodge truck, and an adapter to mate it to the Dana 300. Novak Conversions Home would be a good place to research adapters. Does the Jeep have a 258 in it now? (edit, you have the 4 cylinder which has a Chevy bolt pattern) If so, a later 4.0L swap would be a lot easier, and if you put the 258 crank into the 4.0 you end up with a 4.6 which is about the same displacement and will produce far more low rpm torque than a 273.