As above, you are looking at quaiffe or fixit, or the new mullet boxes.

Mullet looks like the best value, quaiffe is the easiest to get bits for though probably as well catered for already.

Diff wise, if you keep the standard ones, you will need to take it steady in first, once you are into the higher gears the diffs are under less strain due to the torque reduction of the higher gears compared to first.