X2 on this being thought about before, and the factory did a rwd prototype back in the late '80's along with a couple of fwd turbo, high and low boost. Pretty sure the rwd used a GN drivetrain and a Corvette style rear end. Personally I have toyed with the idea of locating the fwd drivetrain to the rear, but have never pursued it. Over the decades there have been variations of fwd GM cars that people had located a second fwd drive at the rear so it was twin engine. All that aside, the most practical way to do a rwd conversion is to find an existing rwd vehicle with a reasonably close wheelbase, or one that could be modified, and imbed that into the underside of a Reatta body. Along the same lines, one of my all time favorite cars I have seen several times at the GS Nationals in Bowling Green KY, is a bright yellow later model Corvair with a 455 Buick engine up front. It runs consistent 10.x 1/4 miles, is quiet and extremely stealthy. So well done you would swear it was factory. It was done by putting a different chassis under the Corvair body. Just my $0.02