The engine is most likely an Allison 1710 which was used in early P-51s, P-40s, P-38s, and a few other aircraft that were designed for in-line liquid cooled engines.
In the early days of drag racing and salt flat speed runs a number of enthusiast tried using aircraft engines from WWII aircraft. The Allison was not in great demand for aircraft enthusiast as the Rolls Royce engines were far superior, so the Allison engines were a "dime-a-dozen". The lack of performance was not the fault of the engine manufacturer. Allison gave the military exactly what they ordered.
Note: You can find Allison engines in Deusenbergs and Auburns, as well as other autos of the 20s, 30s, and 40s. The engines can also be found in trucks (today).