Leica deliberately made the M cameras one millimeter thinner than the LTMs, so that a 1mm thick adapter would put the LTM lenses in proper register on an M body. Unfortunately, you can't put an M lens on an LTM body, for the reason JHutchins pointed out.
The good news is that you can use Leica R glass on Nikon SLR bodies, at least in some cases. I use several Leica R lenses on my D700. I had to remove the bayonet rings and replace them with ones made for the Leica-to-Nikon conversion. You lose auto diaphragm action this way. My 90mm Elmarit, 135mm Elmarit, and 180mm APO-Telyt are all in Nikon mount. My 35mm Summicron-R would not focus to infinity with the bayonet conversion, so I had to sell it. And there is even a Hasselblad lens to Nikon F adapter! No auto-diaphragm action there either.