Post pics if you can Jerry.
I think I have a photo of a RAF MkIV panel. From memory, there wasn't much difference, apart from those switches etc for radio and navigation/IFF use etc, and I'm farely sure that American instruments were retained throughout. If you're fitting the K-14 or British GSGS gun sight, then almost all of the instrument panel is hidden beneath the bulk of the sight anyway. Also, I'm not sure if the yellow tape, around the blind flying instruments, was there or not, as I think this was normally applied, for American-used aircraft, at the BAD, and wouldn't really be needed for RAF pilots., although including it wouldn't harm.
At a guess, the two panels will be for early and late model 'D' versions, but not sure about the seat. But, US Mustang pilots used a back-pack parachute, whereas RAF standard fighter issue was the seat-type pack, requiring a deeper seat pan, compared to that used for the dinghy pack on USAAF aircraft, so there might have been a new seat for that use. Again, I'm not certain, but I don't recall seeing, or hearing about, a RAF back-pack 'chute for fighter use at that time.