These plastic trucks with the motor in them, the entire assembly is below the frame, isn't it? Just a small hole in the frame for the mounting stud? Could you not remove the truck from the GP7 and use the same hole to mount the plastic motor truck in its place?
Re: glue: Loctite sells a two-part "plastic bonding system" that might work. I found it at Home Depot. A small bottle and a cylindrical tube together on the same card. Both are purple.