GT Autostream

Those are nice bikes and they are steel, made before GT gave up the ghost.
Personally, I'm not crazy about the HT kits particularly with the 700c wheels, but that would otherwise make a good candidate for a motor assisted bicycle.

I think the autostream or similar model with manual shifting can be a good 49cc motorbike. If you hop up that motor, you will definitely need stronger spokes in those 700c wheels. Some good cyclocross wheels may be strong enough.

This is what her auto stream looks like and I gotta say its one of the best bikes I've built. I liked it so much I found another to build (the blue one) and its currently for sale. Unfortunately the schwinn landmark meet its death but thank God bokuza is quick and bailed off the bike before the car hit it and didnt really get hurt! The frame broke in four different places! Just in front of the front motor clamp but not at the hole (which I didnt drill) it also broke at the seat post tube and the two smaller arched diameter tubes also cracked. Bokuza'a next bike is going to be an old school schwinn chromoly framed mountain bike- from when schwinn meant quality. I think I'll stay away from steel frames from now on. Chromoly is where its at.