I have a 39 conv. cpe that I converted to power windows. I did a lot of research on the subject due to the fact that most of my friends had poor luck with the units they bought for their project cars.
The units I used were made by a company called Nu-Relics (Nu-Relics.com).. When you look at their web site you will note that Nu-Relics makes a complete duplication of the stock window operator, they then adapt a GM gear drive assembly in lieu of something made out of plastic or cable drive. Nu-Relics also uses GM type switches which do not require relays, etc.
The windows in my conv't are very heavy metal framed units, therefore they need a good power source.
I have used the Nu-Relics on two other car projects. The window run channels are available from Drake, Carpenter and C&G, to name just a few.