In February of 1948 Allan Keyser filed a patent for a side mower. It appears this became the design for the K And K Manufacturing Company’s Mower as seen in the brochures at bottom. You can view other early mowing apparatuses here.
“This invention relates to a mower attachment for the presently popular small, four-wheel drive, automotive vehicles popularly known as jeeps, and has for its principal object the provision of means whereby a mower bar can be quickly and easily attached to, or detached from, the vehicle so that it will be easily visible and easily controlled by the driver of the vehicle.
Another object of the invention is to provide highly efficient means whereby the angle of attack of a mower bar may be adjusted to suit the desires of the user and the requirements of the particular crop being harvested.”