Are you making a tunnel of some sort for the driveshaft to ride in? There has to be somewhere for it to go....and I'm not aware that there is anywhere. The hump the shifter sits in only goes partway back with the exhaust, and then 90s off towards the passenger side of the car, then again towards the back. Also, I don't believe the firewall is configured to allow room for a RWD transmission, so some cutting and shaping will likely have to be done. Now, the 4ws shaft rides above all this, so you might be ok to have both at the same time, but like you were saying, it depends on the where the diff pumpkin has to go....I unfortunately don't have the answers for that - I'm not sure where you're going to put any of the RWD setup, to be honest, but it has been done before - I remember seeing the thread for it. However, I don't imagine it was done without a cutting torch and a welder. There's probably LOADS of custom work to be done to make that work. Sounds super cool, though! Good luck!