Sure there was some chatter about this when N251A was bought over to Flying Legends at Duxford one summer a decade or two back. Pretty sure it was agreed to be an A-36 Apache. Rattling around Woking's pothole infested roads on a bus at the mo (complete with screaming kids...) so not really in a position to research, but didn't the A-36 have dive brakes fitted which set it apart from the P-51A...?