Stay high and stay fast. Frank won't hang with ANY Hog in high-speed maneuvers, especially involving roll--although the F4U's rate of roll is among the best at any speed, really challenged only by the 190s and Spixteen. The F4U's instantaneous turn, particularly with Der Uberflappen deployed, appears to be marginally superior, and she WILL turn inside the Ki-84 at full flaps. However IMO don't ride your flaps. Practice learning when to drop a notch for that extra bump of the nose to get a snapshot. Set your guns in close range and GET in close. At 200yds the Deuce is lethal.
Oh, and the only way the 84 will catch (or lose) the F4U in the zoom is if she has too much of an E-advantage already, however even that's dicey. The F4U has too much mass behind her for a Frank to count on that.
Also, with equal energy states and unless he's already parked 400 yards off your six, the F4U will generally lose the Frank in a spiral climb.
Use your rudder, especially coming over the top of high yo-yos. Can't stress enough the Hog has one of the most effective rudders of any fighter, especially in vertical maneuvers. Kicking hard rudder and dropping a notch of flaps to help swing the nose over and give your playmate a nasty surprise.