To recover from flat spins in pony I always trim the aleirons to one side, rudder to opposite of spin and cut engine. Plane usually drops the flat spin and enters a normal spin downwards, turn engine on shift-X you're out of it.
In P-38 its much simpler to recover. Just turn off ONE engine and plane will immediately spin downwards, engine on, shift-X... you barely lose 3 or 4k doing it.
I've never had a "killer stall" in 38. All the times I have something like that is during combat when the damn wing seems to develop a massive airbrake and spin your plane faster than a 190 on steroids. Once you get one and recover, you'd better RTB, cause it seems to get stuck, any turn you do, no matter how soft, may pull you into another spin. Its really annoying.