When Contemporary was still in bussines they replaced free of charge the two control arms for the Jag rear end. I still have them, completely new in a box. They were reinforced and it seem that Burtis was aware of these problems many years ago, thus the free replacement.
I never got to put those control arms into my Cobra, but prefered to get a complete rear suspension from AMP , which works very well, with a bulletproof billet aluminum control arm. Check out
http://www.cobraracing.com/index.html