The stock case is cast and quite thin in places. When running big power and solid mounts the rear diff case can crack or break with the torque. This is worse with the small case which is noticeably thinner and doesn’t have the cooling fins like the large case.
The large case billet cover will fit UK/Euro and J spec diffs. B series They have the fixings for the UK spec pump sensor and pipe work.
Cooling fins as stock and much thicker and stronger than the stock one.
The small case billet cover is the big upgrade. It has the added strength from the material and thickness, but was also designed with the cooling fins to match the large case. As there are more small case diffs around this is a great upgrade for it. Will fit auto and manual diffs, A series
These are OEM fitment using the stock bolts, they come supplied with dowels and new breather. The large case comes with blanks for the pump fittings if not required.