To recap, my version of the Ventura 66 had a stuck focus ring, and it was not a particularly rare or valuable example. My research led me to believe that the bellows was also probably junk. In short, it might have been worth the $6 I paid for it, but not much more.
It seems that both of these problems are common. The grease used in the helical turns to green goo with age, and the bellows is made of a plastic-coated paper. The threads can be cleaned, but the bellows is more complicated.
I violated a few servicing rules; namely I used more brute force that I should have. I was able to free the lens ring and remove the front two elements. I soaked them overnight in lighter fluid to loosen the goo, then removed it with tootpicks and cotton swabs before reassembly. The focus remains stiff but is now functional.
I took the camera into my darkroom and illuminated the bellows from behind. It was very holy, especially at the corners. The proper solution would be to source or make a new one. I may yet do that, but for now I coated the corners and edges with Plasti-dip. After drying overnight, the bellows was again light tight.
I loaded a roll of HP5+ and took it out for a spin. The fast film allows for smaller apertures and larger depth of field, thereby making proper focus less important. Unfortunately, the first test roll died in the same catastrophe that befell the Bronica.
Undaunted, I loaded another roll of HP5 and tried again. Results coming soon.