There are a few production applications in which the VR6 was longitudinal. The Audi B5 and Phaeton are two examples so I wouldn't think that would be an issue of what it was designed for. Efficiency aside (added engine weight) it would just a engineering nightmare to shoehorn it in there I think. Past moving the mounts back maybe 1 inch (pending axle binding issues) I think you would still have to push the bay forward into the fuel tank area.