I have the LTM version of the 35/2.8, and use it with adapter on an M body. Except for the minimum focus distance, there is no difference in barrel design, DOF scale, or optical formula. In fact, some early M versions were factory upgrades from LTM. You can expect to pay 50% more for a genuine LTM.
Rico Tudor. Leica M4, IIIb, 28, 35, 50, 90, 135, 280. Contax T, RTS; Canon; Nikon; Profoto