Searching will be time well spent. This forum has a lot of good info on it to answer your questions. Welcome aboard.
First things first... Why do you think you broke something in the rear? What axle do you have? What gear ratio do you current have?
Depends on what gears are in your axle now, but you will most likely need to change the entire inner assembly in the axle. You will also need to do the same in the front so that you have the same ratio front and rear.
'78 Scout SSII - 345, 4 speed, SOA, locked, 33's...
'06 LJ - 3" lift, 33x10.5R15's, Discos, TrueTracs, 4.56 gears...
'80 Scout II, '89 YJ, '79 Scout II, '93 YJ, '01 TJ, '00 Cherokee - all lifted, most locked and all wheeled