Thanks for all the replies.
Tim's and John's ideas are really in line with what I want to do. These options are true camera backs.
It looks like the Recomar backs are cheaper than RB backs, and also would not require as much modification. Then again, an RB back can go on an RB as well. Tough choice.
The most limiting factor here is the distance from the lens to the film. Not enough room for a mirror that will show the whole image circle, which is why I want the glass.
If adapting the lenses to any existing still camera, I am obviously going to need a deeply recessed adapter. I had counted on that for sure.
What I am thinking of doing now is to adapt a Recomar back to a single Sinar Multipurpose Standard mounted on a six-inch rail. Put the lenses on a custom lensboard that sets them at the proper distance. Since the camera uses the same connection device on the front and the back of a standard, lensboards can be mounted where you would normally attach the bellows. The camera would look like a pancake. I would also eventually want to design a way to extend teh lens to focus on very close objects.
I could either use a front-mounted shutter, or ND filters and a black film box for a timed exposure.
Sounds fun. Thanks for the help!