I just bought a used 180mm Symmar-S in Compur 1 to mount on a 6x17 Fotoman. I made sure that it came with a retaining ring because I thought it was pretty much all there was to it, instead it seems that it needs a spacer, i.e., the one typically used in Copal 3 lenses between the front lens / shutter and the lensboard. In fact, a screw of the Compur 1 aperture mechanism in the back makes contact with the board and when I tighten the retaining ring it becomes pretty much impossible to change the aperture because this screw is pressed against the board and blocks the aperture mechanism. Hence, my conclusion that it needs a spacer.
The problem would show up on a standard GF lensboard as well, so I am wondering if owners of Compur 1 mounted lenses have a way to get around it, or they know who sells this spacer. I looked at SK Grimes site but could not find such a spacer for Compur 1's.