A guy called Kim Mather used to rally a twin engined Scirocco some years ago. He did a similar thing, just welded a complete unit including subframe etc into the back. They used a manual gearbox on the front motor and the auto box on the back one looked after itself. The car was unbeatable and was up against Metro 6R4's, Chevette HSR's etc.
I'll dig out some pictures and post them up tomorrow.
[Edited on 10-12-2005 by rockhopper]