Surfing the internet, I found this site, which sells power window switches that are operated by your window cranks. You attach your window cranks to the shaft, which is really a hidden switch. So, your Speedster/Roadster looks like it has manual windows, but moving the window cranks up or down activates the switch that makes your power window go up or down. Pretty neat, eh?
http://www.ballsrodandkustom.com/electric2.htm
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