Surefire's incandescent P, C, Z, and G series bodies are all compatible with P60 dropins. The standard bezel for these bodies is the Z44, so the simple answer is yes.
Nope, if you are using the stock M2 bezel there isn't any difference in the reflector size between that and a C2 bezel.
The larger M2 head has a shock absorption layer inside to help with recoils when mounted on a weapon.
However if you are talking about OverReady M2-DD, there is a difference because they use a larger reflector inside the larger head by removing the original shock absorption layer.