A truly beautiful restoration!
In Issue 9 (Jan 2003) of Ferguson Furrows magazine, Del Gentner and I wrote an article about the M-H-F 45, a prototype of a propane-fueled tractor, otherwise mechanically identical to the F-40 and the M-H 50. 15 to 20 prototypes with high wheels were built and tested on farms in Georgia and Texas. These were not production models. When testing was done some of these tractors were rebadged and sold as F-40 tractors. Engineering approval of the M-H-F 45 was signed on April 12, 1957 but the 45 was never put into production. A few months later it became a propane version of the MF 50. There never was a production model of a F-40 propane, however.
Anyone interested in a pdf copy of the story can e-mail me at pnelson239 (at) aol.com and ask for a copy (3 pages).