Have looked at a WW2 aircraft book from the library, and as best as I can tell from the views shown for all the planes, the P40 seems to have somewhat straighter (more parallel) sides. Of course the illustrations may not be completely clear with their shape depictions. The book is "Aircraft of World War II" by Francis K. Bacon.
Views that look possible include planes in the Grumman line - the F4F, and
F6F; Hawker Hurricane MKIIC, B25 lower panel, Northrop P61, and even The Spitfire??
Does anyone know if the P51 D windscreen (that shows a curved bottom edge) in the illustration may actually have a straight lower edge, and that only the frame shape is curved? From a manufacturing standpoint, it would seem easier (less expensive) to fab a straight edge on the thick laminated glass...?
The lower side parallel sections on my windscreen are what make identifying it so much more difficult.