After a good deal of searching around, I've come to the conclusion that I need to find a used helical extension tube in whatever mount I can. I can find plenty of cheap bellows units but I'm concerned that they might cause dust to get inside the camera. I am, however, intrigued with the idea of rear focusing that the bellows might make possible. If it find one with tilt/shift, I just might change my mind about the dust.
In the meantime,I've found a 55mm reversing ring that will let me use my old FD 50 1.4. I've always liked that lens and it will be nice to use it again.