I do not know if Zork did the conversions, but that would not surprise me. They offered several lenses in converted mounts for general sale back then. I bought a nice Zork converted Mamiya 55mm shift lens in Hasselblad-V mount, it's not that unusual for them to show up used. P6 vs SL66 Sonnar The CZJ Sonnar 180/2.8 appears to be made with the SL66 in mind, all the controls are forward of the tripod mount, so even for the factory, they just have to change the rear barrel behind the aperture ring. This is also true for the 300mm Sonnar and the 120mm Biometar. All 3 were listed as a catalogue item for the SL66 at one time, so they will show up on the used market every now and then. You blank Rollei mount was made primarily for macro and LF lenses. Converting a 180 Sonnar would entail machining a new rear barrel, at which point you may as well machine the rest of the SL66 mount.