The trek rigid bikes with threaded bottom brackets and quick release wheels are tough as nails for regular bicycling. If they have good condition wheels and tight spokes, they should be excellent but rough riding for motoring. I agree that you should compare the motor producer's spec sheet with the dimensions of your individual bike.
I had one as a teenager, and it was very durable. It came with low end shimano stuff from yesteryear, but parts are easy to find on Nashbar.com