a) go for a 126 body diff with a 2.88 ratio (anything from 1982 -85)
b) piece of cake, 15 min to remove each side axle stub, 40 min or so to remove the center pumpkin (already drained if you got the C-clip off) and another 3 hrs to batten the hatches and fill fluid
GO for it !!!!
email if you're stuck....
pps- If you cannnot get the fill plug (14 mm hex socket) off before you drain the diff, stop and DO not proceed !!!!!!!