"Just think, they could have done the B with the early style, done a C with the Malcom (no dif then the B but from the Dallas plant) and the D."
If you want a P-51B and P-51C to have different performance, model one with the V-1650-5 engine (which the current AH P-51B has) and the other with the V-1650-7. Both models were built with both engine types, as the switch was made partway through the production run. More P-51C's than P-51B's were built with the -7 engine, largely because the P-51C remained in production longer than the "B". The P-51B as modeled in AH seems to represent a P-51B-5-NA.
It's also worth noting that the Dallas plant built both P-51D's AND P-51K's.
Optionally, an Allison-powered Mustang (Mustang Mk. I ideally, though a P-51A or even an A-36 would work) would fill an even larger hole in the AH planeset. Such a plane would doubtlessly have the old-style hinged canopy.
J_A_B