As I said, late-war perk fighter, better than the F4U-4. 3 planes and a lot of trucks. Package it up any way you like, but snake oil is still snake oil.
And I think the thing you're missing here is PERK fighter. Perk plane usage almost certainly accounts for less than 10% of total activity in the game. Drop that 98% back down to a 9.8%, and it would be more accurate.
If added, the P-63 WILL be perked, no ifs, ands, or buts. It will also have the misfortune of having an annoying gun package for most of the players in the game. It will also be vulnerable to planes like the K4, La-7, 190D9, etc, making it even less attractive, since most players would be simply writing a check for 25 perks on take-off.
This caters specifically to the P-39 crowd, and nothing more. It doesn't add anything but a 37mm cannon to an F4U-4, and everyone will fight it as such. Actual flight characteristics will certainly be nothing new; fast, climbs good, pretty maneuverable. Attributes shared by the F4U-4, La-7, and the K4 to a lesser degree. There no way to reasonably justify its addition in the near future over so many others that has so much greater impact, and simply did so much more.