Dave Ware writes: This is the Rolling Lift Bridge model from a #10 1/2 set manual.
The bridge has a swinging basket in the rear for adding weight to balance the bridge. Counting holes on the diagram resulted in a mounting for the basket that hung up on some screw heads. After some changes, it worked fine. A magnet from a speaker was used for ballast. The method of mounting the motor was not specified. I’m sure that my solution is not the correct one.