Manufactured between 1929 & 1939, these side delivery sickle mowers were extremely popular in their time. Originally horse drawn, this one has had its wooden drawbar removed (or it rotted and fell off), so it's going nowhere in a hurry. Ground powered, in a heavy hay crop they required a fair amount of strength from the horses and were difficult to use when the ground was damp or wet, as the wheels were unable to gain traction.
Have a peek at this
Farmall sales brochure, date unknown. Mowers are on page 28.