The High Planes 1/72 Mustang Mk.X. The kit comes with three (or four) configuration options which covers all the prototypes. I built mine with one of the upgrades the Mustang Mk.X got but is not in the kit. Wind tunnel tests had determined the fin didn't have sufficient area but I'll have to re-read the book to find out what it was, but it involved adding a 3" wide fin leading edge extension, from fuselage to fin tip.
RR received five surplus to requirement Mustang Mk.I's (Allison engine), one was kept in original condition so RR could do direct comparisons with the Merlin conversion. My build is of the final configuration and had a Spitfire Mk.IX engine, prop and spinner.