The Tamron made, in the past, two different Adaptall-2 adapters for Leica SLR (one manual and one automatic, dedicated to the Leica R cameras). These special adapters, maybe still available (see at italian importer Rossi & C or USA importer for real availability) request another adapter, to mount the bayonet Leica R on the bayonet Leica M, but lack the rangefinder coupling (remain, vice versa, the infinity focus capability). Naturally, this system is good only for the wideangles, used in the hyperfocal focusing.
The same opportunity exist for the Canon FD or Nikon AI Adaptall-2 rings (easier and cheaper to find).
Ciao.
Vincenzo