ShuRugal-"well, unless the plane has an AoA meter, the pilot has to use things like IAS and known aircraft weight to judge when airflow separation will occur.
since the P-51 lacks an AoA gauge..."
No, all you have to do is watch for signs of an impending stall, this technique works at any speed or aircraft weight, when you see/feel the buffet ease up on the stick. :)