I know it's not an E-type, but check out ERA's web site which shows the process they go through to prepare the Jag XJ6 rear suspension for installation into their Cobras. Basically, they shorten the lower control arm and driveshafts which also act as the upper control arms to get the original Cobra flange-to-flange dimension.
And by the way, I just acquired an XJ6 rear suspension setup bolted in the cradle with brakes, center section and suspension with shocks and springs intact. I'd be willing to part with it at a very reasonable price. Got it to have a spare just in case.
Here's the section on Jag modifications in ERA's web site:
http://www.erareplicas.com/427/shorten.htm I hope this give you an idea of what to do.