Good catch there Glenn. I've spent ages trying to figure out which kits give the correct intake for the RAF versions - rather confusing at times!
Here you go Terry, put together from my resent research:
ALLISON ENGINED MUSTANGS
NA-73X
One of a kind prototype. Short, narrow carb intake and variable radiator intake. no guns, but holes for two under nose guns and three in each wing. Looked pretty much like the early Mustang I's with the short carb intake.
XP-51 = Mustang I
Two Mustang I's from early in the RAF order were supplied to the USAAC as XP-51's. The early ones has a shorter carb intake which was later changer to the longer ones. They also had variable radiator intake and bulged fairings that the under nose guns came out of. Guns were two .50 cal under the nose and one .50 and two .30 in each wing. One XP-51 is on display at the Air Adventure Museum in Oshkosh Wisconsin.
P-51 = F-6A = Mustang Ia
Straight, narrow(when viewed from above) carb intake and variable radiator intake. Two 20mm cannon in each wing and no under nose guns.
A-36
No RAF version although one supplied to them for evaluation
Dive bomber version with dive breaks on upper and lower surfaces of wings. Carb intake wider with straight sides when viewed from above. Two .50 cal in each wing plus two .50's under the nose with out the bulged fairing. Fixed radiator intake, although of a different design than in the Merlin Mustangs.
P-51A = F-6B = Mustang II
Wide carb intake with curved sides when viewed from above as in the A-36. Fixed radiator intake also the same as The A-36. Two .50 cal guns in each wing. No under nose guns.