RE: is this a 51D painted like a p40 warbird?
You are probably right that the nose is "too long" but then, it doesn't appear to be a truly scale model of a P-51D anyhow.
The other comments about the "tiger/shark mouth" nose art are right - we associate this with the P-40 only because of the fame of Claire Chenault's "Flying Tiger" squadrons that supported the Nationalist Chinese army against the Japanese in the early part of WWII. Such art was even used on a few bomber types - I've seen a B-24 with the grinning teeth below the nose turret.