There are a few choices. One is to get a Rubicon D44 core and put your own carrier in it. You'll be able to reuse your outer knuckles, outer shafts, brakes, etc... Then all you'd need to do is get gears and the inner shafts. That would probably be the easiest.
Next option would be to get a D44 from something like a SJ or a Early Bronco. These will be the wrong bolt pattern for your rear axle. You'll need to either get adapters and run new wheels or else drill the flanges and run the larger pattern. Best to go with a SJ since you need to upgrade both axles anyway.
Other option would be to go big and get a D60/70 combo from a Ford F-350. You'd be going full width but you can fix that with some negative offset wheels. This would be equivalent to you running 3.75" BS on stock axles. Not cheap but a good increase in strength.
Also, if you're planning on going with super low gears like an Atlas 4, Klune or and engine swap, then you'd be better off with a D44 then a 30.