P51D had the Merlin. We sold a lot of P51Bs to the Brits with RollsRoyce engines in em (they had the birdcage canopies). They were not up to 'D' standards but they were still the best escort fighters the Brits ever flew.
UK quoted soldier:
"The problem with you Yanks are you are over-paid, over-sexed and over here" ....
US quoted soldier:
"The problem with you Brits are you are under-paid, under-sexed and under Eisenhower" ....