OK. Here's where I'm at on the bellows...
The pigskin is quite thin and has a suede surface. It was the closest thing to the original that they had at Tandy. Unfortunately, it had pinholes throughout. The young woman explained that these were follicles and all of their thin leathers would have them. She said that some animals could have fewer (perhaps goat) - but there were no other skins in stock that were as close to the original bellows as the pigskin. I couldn't wait. Pigskin it is.
She suggested I seal the pores with Johnson's Floor Wax (!?). She said that mink oil might work but would leave a residue that could rub off. They only sell leather by the "skin" so I had plenty to experiment with. Wax does not work. I then tried Camp Dry silicone leather spray with a dark furniture wax over the top. The idea was the silicone would plug the follicles and the dark wax would stop the light. Did not work. Then I tried Plasti Dip. I think it worked!
I found the Plasti Dip at the Home Depot next to the spray paint. It comes in different colors- I opted for black of course. The container resembles a small tennis ball can. I used a small brush to apply it. Put the first layer on liberally brushing in one direction. Waited about 30 minutes then applied a second liberal coat across the grain of my first coat. Let it dry overnight. Now the pigskin has a layer of rubber on the inside similar to rubberized light tight cloth. The rubber appears to be of a decently lasting quality. For clean up and thinning of the Plasti Dip I used naptha (lighter fluid). Do keep this in mind if you use naptha to clean the camera mechanism as it can melt your rubber layer. The pigskin did lose a bit of its flexibility, but it still seems sufficient for a Panoram bellows. Also the rubber dries with a glossy surface- I would prefer matte. I'll update after I mount it in my camera. should have some time for that next week.
The Plasti Dip might also be a good seal for those of you that are needing to fill light leaks around the doors. (I swear I don't work for these people)
For reattaching the exterior leather I've been using Orange Shellac. It can be removed/cleaned with denatured alcohol. This doesn't make the bond as permanent as glue, but has sufficient strength. Orange shellac was traditionally used to hold pen sacs in fountain pens,so pen restoration suppliers would be where to look for this. I ordered a small bottle of this product from Pendemonium. It was inexpensive.
I'm mulling over the adapter/shim for a better 120 spool fit. I am going to be building adapters to fit 120 in my 4-D so I'll be exploring that soon. Perhaps some gaffer's tape for a quick fix fit. Let us know if you come up with anything. I'll update after installing the bellows - prob. at the end of next week.