When I was in the process of installing the Nu-Relic electric windows in my 39 convertible, I had to send the original window regulators to Nu-Relics, they made new regulators that were an exact duplicate to the original regulators, the difference being that the new regulators were modified to accept the GM motor assembly.
The one problem I had was that the doors for the early model vehicles are not built strong enough to accommodate the added torque that the electric windows puts on the doors.
I had also added electric bear claws door latches which added to the torque within the door.
Within a few months I noted that the lower portion of my doors was protruding beyond the 'B' pillar/rear quarter panel, and that the doors were not closing smoothly.
We took the doors apart, fabricated some struts out of steel, which were attached within the doors once the doors were pulled back into alignment. Problem solved the doors close like a refrigerator with hardly a sound.
Foot note: I installed "Road-Kil" (Dana-Mat) to the inner side of the outer door panel prior to installing the window operators.
The windows in a '39 convertible coupe are very heavy, Stainless Steel framed similar to a later model vehicle.