Ki-84 vs Hellcat wouldnt be bad, it really depends on the pilot. The Ki-84 at low speeds is very tricky until you get the hang of popping the flaps down. Without flaps deployed, a slow Ki-84 is lunchmeat for a well flown Hellcat.
Dont sell the P40E short either vs the Ki-61. Of course, I'll always be happy with any setup that includes the Tony. Once the Tony gets some speed up, its dangerous, and even at slower speeds it's nothing to sneeze at. I feel fairly confident flying a Tony vs an average pilot in just about anything else. You arent going to run away from it in a P-40. But I've seen some of the guys in here make a P-40 do some incredible things down on the deck.
I'd go along with a A6M2 vs Hurricane I matchup also. These two are close enough to make for some nice fights. The zeke holds an edge, but a good pilot can make the difference to even it up in a Hurricane.