The motors are bolted while the regulator is riveted.
The power door lock is grounded on the drivers side. There is no ground on the passenger side. Running a ground from the power door lock ground on the drivers side should improve the ground for the power window on that door, but it does nothing for the passenger side. To ensure good ground for the power windows, it would be better to ground both motors to somewhere under the dash. It would also be better to ground that power door lock circuit like Brian suggest above. At least from what I read, that's what I understood Brian did....but I did read it quickly.
There seems to be a common misconception that the black wire connected to the door grounds both the door lock and power window circuits. However, that ground wire near the drivers door handle is actually the ground point for the power lock circuit.