On 756990, the patent on the hammer is original. The stocks are indeed not correct, but neither will be smooth Victory stocks. The gun is from early 1941 when the pre-war small checkered-wood stocks with silver medallions were still used. No property stamps were applied at the time. The P is the standard military proof; this was a British Service model purchased by the British (or allied country). The fact that the hammer and trigger are the same finish as the gun and that finish looks different from the original Carbonia blue indicates a refinish.

The US Victory is from early 1944, looks all original and without property mark would indeed most likely be a DSC contract gun.