Not sure of a good donor vehicle, but with all the room inside the door of a '54, you probably could just measure the width of the bottom of the rail lift and go hunting for almost anything. You'd still have to fabricate mounts and brackets to hold it onto the inside of the door, plus wire it, get switches, etc, etc, etc.
In the long run, you might be better off contacting A-1 Electric and see what they have: www.a1electric.com
At least then you know you're getting something new, that works, is pre-wired, and will install easily versus trying to ramshackle your way into PW's.
Unless you get something direct fit, aftermarket power windows are a big pain to install. My experience is limited to two different kits. They were both very time consuming, requiring fab of every bracket.
if your windows go straight up and down Hyundai Steller rear power windows work great. They are 2 wire motors (reverse polarity for up and down ) same as GM so you can use GM switches. I used them in my 59 Merc.