After tearing down and restoring an old 70's Schwinn road bike from scratch and maintaining a fleet of 5-6 bikes of various types, I am looking for a more challenging winter project. Buying a moped or scooter would be nice for getting around town more quickly, but that would be too easy. I race mountain bikes and am very comfortable on a 26 inch front suspension build, so I am looking at buying an older steel frame mountain bike and retrofitting a motor. I would prefer USA made kits/parts and am leaning towards a center frame-mounted motor for better balance and center of gravity. I am in the very beginning of research into this, so any help in the right direction is welcome. Thanks!