The SW looks suspiciously like the Model B.
I wonder why they introduced the Slant Window so late in the model run?
M2M is from Australia, and there were originally no 31's in Australia. So a 31 of any body style is a rare vehicle here.31 SW (SW = Slant Windshield) isn't all that rare. They were made in the latter part of 1931, and you can see them everywhere.