Showing my age here but I remember a Mini in the sixties that had a Buick V8 engine (foreunner of the RV8) in the back, in place of the rear seats driving a Jaguar E-type diff in the front. Can't remember how successful it was, but I bet it cured the understeer!
Great project and all the best with it, you'll love it when it's on the road...............even my little fella makes Scoobies with 555 splashed down the side wish they'd behaved more civilised and not try to show me what a modern "rally car" can do to a poor little mini