I would have thought (I'm no expert!) that prop RPM and power settings would provide a good clue if the ASI was a problem, plus being familiar on type he would have some "seat of the pants" feeling to whether the aircraft was slow or not.
After going out of control the first time a pilot would have considered the likelihood of a problem and probably got on the the R/T and the ground ASAP. That he didn't, plus the application of pro-spin controls immediately prior to the stalls (which sounds to me like over-controlling while counteracting torque as the aircraft slowed to the stall), indicates some sort of incapacitation IMHO.
Any experts out there confirm these thoughts?
Ever see Guy flying the P-63 in tight formation on Steve Johnson in the P-40 at the Duxford Flying Legends shows? A great pilot...