Well, I've slept on this and it looks simple - too simple probably!
Parts needed would be:
Tube of right length with flanges either end to hard-mount the two mounts
A Leica M-mount (screw to M adapter would suffice, or I assume a proper mount is available as a spare part? Or cannibilise from a dead lens)
The lens mount removed from a donor Ambi Silette. This page
and this one
indicate that its reasonably easy to extract the mount and shutter assembly.