don't forget that tube diameter is relative to roll. thickness of the tube is usually matched to the vehicle(ie- sprung weight, weight split)its like a giant swaybar/torsion bar.
mx5 diff would be easy to mount. early ones are easy to get and all imports had lsd( only aussie 1800's had lsd) usually cheap too because mx5 guy like to update to later model torsens(nb series).
what size early camshaft are you after?