I'm swapping out my rear axle with a Ford 8.8 from a 1998 Explorer. I'm installing the Superior Axle "Super88 Kit" as well as an Aussie Locker. The axle kit gives you the 5 x 5.5 bolt pattern that you need as well as a bunch of other nice upgrades.
But as far as the easiest swap...Like Bob said, the Scout II rear Dana 44 is the easiest option. If you can get your hands on one.
'77 CJ-5 Renegade 304 / T-150, Dana 20, 30/20 axles, Aussie Locker in the Dana 30, American Racing 15x10 Outlaw II's, 33" Dynapro M/T's" ,Optima Battery, TeamRushed + Summit Racing CDI ignition, FlowKooler water pump, Edelbrock Performer Intake Manifold, Holley 4160 390cfm, Herculiner, Silver Ceramic Coated Hedman Hedders, Flowmaster 40's.
Warn PowerPlant HD 12K Winch, Dirtworx front and rear bumpers.