Most reproduction Shelby Cobras use the rear from an old Jag. Think the 78-87 XJ6 sedan or the 78-94 XJS coupe. The rear will handle the torque of a V-12, and a 428 side oiler, so I think it could handle probably anything else you could put at it. The minus is FINDING one of these rears- as many have been pulled already!

Also- in the same vein- Look at set ups that are offered for the Shelby Cobra Kit Cars. If they are using the XJ set-up, then I am sure someone is making a bolt-in that is based on it.
The plus is you get Ford bolt spacing- same as Mopar. Not sure of track width, etc...

Hope this helps!
CC.