P-51A's and A-36 Apache's had three bladed props. The four bladed props started with the B's and C's.Nitpicking here, but every P-51 I've seen (and that's a lot over 47 years of Reno Air Races) had a four-blade propeller, nor can I find one in a photo with three blades. And those blades seem too small.
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Added: You see the P-51A above. And, yes, they saw combat. The "MUCH lesser known A-36 was a P-51 fitted with dive brakes and a 20mm cannon under the left side of the engine

You can tell right away what a model is by A. number of blades on a prop and where the intake is. The V-1710 Allison, the air intake is on top of the engine, the V-1650 (RR, Packcard, even Maytag) the intake is on the bottom as seen on @Mills shot of TOULOUSE NUTS.
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