[David603]

Interesting if they did. But I wouldn't understand why they would degrade the aircraft.

I'd heard some P51Ds were converted in the 80's and 90's to run cheaper and more widely available Allison engines, and I was interested to find out details.

Anyhow, I'm not sure it would be a downgrade. By the time you have taken out the guns, armour, surplus fuel tanks and WWII radio equipment the P51D is around 2,500lbs lighter, and the V1710 is still a powerful engine at low altitude. Plus the V1710 is lighter than the Merlin, so you get another weight reduction by fitting it. By the time you were finished, you will have a plane that is at least as fast a WWII P51D at low altitude, while being a heck of a lot lighter and more pleasant to fly.