A SJ410 would be close to bolt on, I know a guy that put the diff out of a 83 SJ410 under a 79 LJ80, my 82 SJ410 diffs are 50" wide drum to drum, 83 and up have disc brakes on the front diff, 82 and older have drums front and rear, but I think they are all 50" wide and have 410 R&P gears until 85 then they changed.
With the 83 front diff you would get the disc brakes and your LJ drive shaft bolt pattern is the same, in 84 they changed the bolt pattern.
Hope this helps.