The P51-B was built at Inglewood, California the P51-C was built in Dallas, Texas. The B model was started with the -3 version of the Merlin but soon adopted the same -7 that was installed in the C model, for all intents and purposes they are the same plane, the Dallas plant was hastily built to accomodate the orders that were let after the USAAF was finally convinced it could compete with the current 109's and FW's.