No idea if it's been mentioned.
The P-51'B' in this game is actually a P-51 (with no variant abbreviation; i.e. Not P-51A, just P-51) which is a Mustang Mk.Ia (RAF equivalent)with 4x 20mm cannon. These were requested by the Brits. The plane had an Allison V-1710 engine equipped with a 3-blade prop, noted by the intake on top the engine cowling.
The P-51B's were much different: Merlin-powered, inlet at the bottom of the cowling, 4x 0.50 cals, deeper oil/rad cooling intake. This was the Mustang Mk.III, and is actually considered the best of Mustangs in terms of performance.
P-51/Mustang Mk.Ia/NA-73X
P-51B(C)/Mustang Mk.III
Strange this mistake could be made since the P-51B/Mustang Mk.III was in IL-2 1946 and was favored by many a Mustang pilot.
Everything looks great other than that.