Are all late model (not an antique) Brunswick return boxes the same? In other words will a GC box work on a Medalist?
It wouldn't look right.
See Medilist Ball Box Picture.
Compare it to a GC I, II, III ball box.
Do what they did in the Old Days.......
Use a Basket.
I don't think GC boxes work even on other GC's from different GC model numbers less alone on a different model.
This would be a question for Mark Gregory or The Guru of Tables.
Be sure to bring an offering for appeasement.
If you can find the attachment points you could build a box.
Maybe Classic Billiards might have some drawings or specs or a source for an expensive reproduction.