I think with a spring tensioner on the chain it would be an excellent bike, The rear pivot point looks like you can get the motor really close to the same plane. Set it up with the spring as cranked up as much as possible or if that don't work as slack as possible
The frame is like my Mongoose Paver, kinda contorted. Big mounts and off-set the carb. The motor will set high in the frame. I had to leave off the rear cast mount and made one up from Permatex Epoxy Putty and a plastic baggie. Cleaned the motor and stuck a gob of putty where the frame and engine met, the plastic bag kept the putty from sticking to the frame. The rear motor mount is at a bad angle to meet the seat post tube. After sanding off the finish on the post a wedge of epoxy putty was placed on the post and formed to change the angle the seat clamp has to fit on using a plastic bag to prevent sticking to the bolts or clamp.
That's a real nice bike for free...I just don't understand people anymore