Hi Graham and Malcolm, thanks for the pictures of the massey 12-20's. the 12-20 was not a really common tractor compared with the 20-30. They made about 7000 12-20 and close to 19,000 20-30.  I think one of the main reasons the Massey Harris #12 and #20 are hard to find is because the parts list claims that the MH tractor was made for export. Now we know there were 12-20 Massey Harris sold in the US so I guess it wasn't a rule according to the parts list.  

I just got a massey brochure in the mail yesterday. It must be around 1934-1935 as it lists just the massey model 12, 25 and GP. So here is a picture of the #12 ad. The most important line is at the bottom of the page.