I found that repairs to the chassis are best done with a large paper clip, cut in a U shape, and glued across the back of the chassis (on top). When doing this, do a dry fit (maybe with a small dab of shoegoo) to see if there are any jams with the body. If so, use a razor knife or very precise dremel cuts to trim the body where it hits the paperclip patch. I will add pix later.
"... get on your bad motor scooter and ride!"
Sammy with Montrose