I've got the ICM P-51A too, it's a disaster. Fuselage is for Mustang mk.I/Ia. Narrow carb scoop, flat top of radiator intake. Wings are P-51B but if the stiffeners are sanded off its OK for an A. I'm going to turn mine into a British Mustang I with the Ultracast set. NA-73X is possible, but harder. Lots of different panel lines and you'll need the Falcon vac canopy.
The ICM bomb racks are correct for A-36/P-51A and P-51B though, so save them for another model. Accurate miniatures used P-51D bomb racks because that's what's on the USAFM A-36. Other good features of the ICM kit are the tail wheel, which is installed *after* painting and the Tamiya-clone wing which can be modified to correct the wheel wells more easily than the AM kits. And it has lots of spare parts like an Aeroproducts 4 blade propeller, different spinners, etc.