Juicing up the seafire IIc to a Seafire L III (by far the most common varient) would be nice.
I have flown with a couple of dedicated ROYAL NAVY squads and I think this was the
BIGGEST request I ever heard anytime the subject of RN planes came up.
Sea Hurri might not be a bad one also for early war stuff - really nothing there except the MARTLET/WILDCAT.