Looking good Geo.
One point, although there's probably not a lot you can do about it.
In the ETO, the P-51 pilots used a back-pack parachute, with a dinghy pack on the lower harness that fitted into the seat pan, used as a cushion. This meant that there wasn't a seat back rest cushion.
When the back rest cushion was fitted ( I believe in the PTO and/or later in Korea), it doubled as a flotation device, and was yellow in colour. Presumably the back pack parachute was then replaced with a seat type pack, with a dinghy pack between the pilot and parachute pack.
To date, I haven't seen any evidence of the seat back cushion in use in the ETO, although, of course, this might have been possible late in WW2.