Far as i know, the Revell P51B is the Monogram kit, which has both canopies, although moulded closed. Built a few of these, and it's nice, even if old.
The Tamiya P51D is excellent, and their P51B is too. BUT, the ICM P51B is a clone of the Tamiya, with lots of extra bits, and a lot cheaper. It's the one I used for my D day GB build. It needs a bit more care, but is , overall, a nice kit.
If you need a Malcolm hood, I think I've got one, maybe two, spare.
Cheers, gong to bed now, as in a bit of pain after walking arund in the cold at the airfield today. Plus, it's 03:24 and I'm b*lloxed anyway!
T.