Not an expert, but on these rear ends it's worth adding something to limit the downward movement into positive camber. Otherwise if you go into oversteer it creates a positive camber which effectively jacks up the back of the car and they can flip over, especially if you back off. Pretty much the same as when you highside a motorbike. Some GT6s had rotoflex couplings to help with this. A friend flipped his Vitesse 1600 years ago, there were four of us in it so extra weight doesn't help, still have the scars!! In this example the side of the Vitesse never touched ground as it went straight from tyres to roof so it flipped rather than rolled. Spitfires and GT6s have a lower CofG so don't suffer as badly, so if you're building something lower than a Herald it might help.