It would probably be considerably cheaper, and probably easier to find a wrecked Mustang. Split the pinch welds and take the body off. Do the same to the Contour. Mod the Mustang's floorpan as needed and weld it under the Contour. That would get the fuel tank, rear suspension, trans tunnel, etc out of the way. Adapt the Mustang's front subframe to fit and then work the bugs out of the front suspension.
The one probably I see with a straight axle under the rear of our cars is clearance. You would have to lift the floor a lot to allow the axle to have its movement.
If you want a V8, supposedly the Jag 4.0 will fit. Granted you would still be FWD but from measurements, it will fit.
