Ron, that soft pigskin sounds promising, so I am anxious to find out how it works out. Since you were able to get it already dyed black, I am wondering if they sealed the pores in it? Also, if it works out, we could all use ordering info, such as catalogue number and the ordering address (snail mail & on-line, or 800 number for call in orders). I'm definitely keeping my fingers crossed that you have found the right stuff to use with that pigskin.
Another thing that I have been mulling over is making some sort of adapter/shim type thing to glue, friction fit, or otherwise attach to the film spool spindles to make the 120 film spools fit a little better without being so wobbly. The holes and keyway are large and fit very loosly on the Panoram Model 1 spindles which were made to fit the smaller holes and keyway on the 105 size film spools. I would suspect that the looseness could cause a bit of binding and twisting of the film, which might contribute to the occasional tendency for the film to come out of the track and drop down into the camera.