A few years ago I played around with digitizing negatives and slides using my K-01 and the Pentax Bellows II and slide copier that came with it.
I ran into two issues trying to get the right magnification for the cropped sensor to capture the entire frame.
The problems are the length of the slide copier bar and slide copier bellows and the depth of the fully compressed bellows.
Through a bit of trial and error I was able to get it to basically work. Using a 55mm lens with the bellows compressed as much as I could, and then the slide copier mounted to the very very end of the bar, the magnification basically works, but then the slide copier bellows are to short. Using a hood from a M100/2.8 and gaffer's tape, I made an extension for the bellows and got it to work.