I have completely changed to a toyota 8 inch diff & housing which is considerably stronger to a std rx7 diff. Rally guys I know have upgraded their 2 litre corolla to a mazda diff and regularly broke axle's. They have since changes to the 8 inch toyota diff and have had no trouble for over 3 years.

Yes it is a budget car, as it is so old. If I had unlimited budget I would be running a Subaru WRX or the like. But it is not a budget class, as these rules effectively apply to all levels except world rally cars!! The problem is that there are ways to fix things within the rules, but they are a lot harder and generally more expensive. . In some ways it would be cheaper and easier using anything you can buy off the self/ or make yourself. If it was free I would probably try and stick a independant rear end in there - OK I guess that would cost more than the current restrictive rules

but thems the rules and we have to stick to them.

so just to confirm jgrewe - using spherical joints in the watts link won't cause any binding issues?

Cheers