[fuchs]

Factory retrofitting of a synchro flash system to Leica IIIs was done through conversion into a If/IIf/IIIf type synchronization. The quality of third party modifications was obviously largely dependant on the skills and smartness of who installed it. They involve soldering contacts inside and accomodating wires and contacts and this can be a tricky procedure in such a tiny space.
I have never seen one that didn't destroy the screwmount Leica aesthetics if fitted at a different place that the one chosen at Wetzlar.
You can always resort to a Geiss Sinchro Contakt if in absolute need of using flash on a SM Leica.

Best,

Ed