Don't know the intimate details Milt, just repeating the information as I understood it at the time. The guy was giving some training to another chap in a two seater. Supposedly the trainee put the aircraft on its wingtip and pushed forward. PIC knew about the situation but couldn't react fast enough to prevent the engine going over the red line. As I was told, it was a region of flight (on the wingtip followed by negative g) in the P-51 that was known about and avoided by the owner/PIC.