Tom,

I have the same brochure and a few others also refering to the "12" tractor and as you say 7000 produced in seven years is not high volume.

Here is a photograph of a M-H 12-20 on British cast wheels with rubber tyres which was part of the late Ian Robertson's collection in Scotland and sold in his sale December 2011,
I first saw this tractor with my dad at the Weeting Rally in Suffolk in the late 1970's, it was then painted light blue and eventually bought by a dealer who sold it North of the border to Ian and I understand it went south again at his auction.

Malcolm.