Hi Winslow33,
First of all, call your Spitfire a Mk.IX because that is what it really is. The 4 blade propeller is a dead giveaway and if you flip it over, the radiators would be a giveaway as well. No problem though because there WERE Spitfire Mk.IX's sent to the Russians. The planes that were sent were generally pretty beat (from a book by Alfred Price about Spitfires). Also, from a book (Mushroom I think) about the P-39, the performance of these Spitfires was not quite as good as we might normally expect. Maximum speed at altitude was only about 390.
I didn't think the US ever sent P-51D's to the Russians, but I may be wrong. What I DO know is that the P-51D could never have mounted a gun firing through the propeller hub without some major re-engineering. The Russian Klimov engines used in the Yaks were based on a Hispano engine and had the room between the cylinder banks (and enough offset in the reduction gear) to allow for the motor cannon. I don't believe the Merlins had the room. If someone knows better, please let me know.
- Ivan.