The gun is from mid-1943. The lighting in the pictures makes it hard to tell, but you may be mistaking the original dull greyish phosphate finish for "no finish left"; happens a lot, if you haven't seen a lot of these in natural light. To me the surface actually looks quite good.

Your photos don't show all pertinent areas, but I don't see any post-war British proof marks, which is uncommon. But you are correct that it was a Lend-lease gun which (in the absence of any other country-specific markings) would have shipped to Britain.

Except for the butt. All butt markings have simply been ground off. As Muley Gil has pointed out, in the US, that's bad news. If you can own it legally like that, the price would be attractive, of course.