The P39 wasn't a bad plane,but because the looks of the blower annoyed the Army buyers, it was removed,and the performance suffered greatly.The P63 King Cobra was a different story.It came with better Allison 1710 engine,Laminar wings,and a blower,and now we had a plane that could compete on equal terms with the all the other late war planes.Again the politics got the folks at Bell,and the P63 was relegated to state side duty.It was a quite capable aircraft,and a King Cobra won the 1947 air race at Reno.
One of the major annoyances with the P39's P63's,was when you fired the 37 MM Oldsmobile cannon,it filled the cockpit area with nasty smelling gunsmoke.
The claim that it was a hard plane to fly,was simply not true.One had to pay attention to what was going on,and it gave you your monies worth.
It would be a lotta fun to see a P39-P63 in AH,but I'm sure they'd make it a dog,which it wasn't
IronDog