The R-1820/30 powered Curtiss P-36/Model 75 Hawk evolved into the V-1710 powered P-40.
Who's to say the similarly powered Seversky P-35 couldn't have had a similar evolution?
I'm thinking a V-1710 powered P-43.
I suppose the downside could be no R-2800 powered P-47.
But a potent P-43 could have been nice for the early war years, and could have ended up displacing the P-40 to some extent.