Only problem in re-drilling and tapping the standard case is that there isn't much meat around the holes, so by going for a stronger bolt you weaken the case!
The Quaife thickwall case has thicker walls (strangely ) and M8 holes as standard. You then drill the lid to suit.
As I stated earlier, it is the PINION area of the case that splits, so any action in the area we are currently discussing, is probably irrelevant...