Orignially the gears were turning to weld the doors shut, and then construct a fiberglass hull beneath - hydraulics to retract the wheels. Not having worked out any details at all, I was thinking I would use the 3.4V6 -> 4X4 S10 tranny -> power output to front axle would actually be redirected to a pair of large jetski pumps mounted somewhere? The biggest problem I was thinking was getting the weight down (so it won't be floating near the window sills) and getting the COG to the rear.
Looking into it more, I think that the approach to take would be to start over with a nearly 100% fiberglass body - kinda like the $150k Camaro-looking thing
www.watercar.com