As Hoskins said, getting one in parts is the best bet. I have been rebuilding them for about 40 years now and many people have sent boxes that were simply junk inside. You may get lucky, but watch what you spend on them unless you know what is in it.
Several years ago I went through a 16:21 ratio box that felt very good. When I got it apart there was a missing tooth on the prop gear. Not just damaged; missing!!!! The sad thing is that somebody else knowingly put it together that way and sold it. The point of this story is that even one that feels great can be no good.
Hope this helps some.
Steve Roskowski
