I remember a discussion about body mounted couplers and someone who was making 3D printed boxes for the guts from a standard MT and making it much smaller and compact with great results. I can't manage to find the thread about it and what happened to the project. Anyone remember this and have more information?
I remember a discussion resembling what you're looking for. It's most likely one of those threads that started out with a title that gives no hint to the turn the discussion took.
The only one I remember is this one........... https://www.trainboard.com/highball...e-best-coupler-box-is-here.89213/#post-954441