Olddog,
Jag rears have been used with good results on thousands of replicas (Cobras and hot rods) and tens of thousands of Jags. The stock axles are very reliable and ERA has made them
fail safe. Failure rates from torque application is probably less than the failure rate of CV-type axles, and they never fail from axial loads, which are relatively small.
More information on the ERA rear is
here.
We've found the rear brakes very reliable and the pads will last 40K-miles-plus and the rotors much more.