I beleive that is an "MR" series, which is similar to the "M" series in the pic of my 351, without the break away hitch. The MR seams to have been the "economy" plow because, unlike the MT it has shear bolts instead of mechanical trip bottoms. And, the MR's had a long landside on the back bottom, that extended aft to help manage the side draft instead of a furrow tail wheel. Tail wheels may have been an option of the MR, but I have not seen one equipped that way.
All of the other wear parts are consistent with the other case plows of that vintage, and are generally still available. I've never looked for that extended landslide....but would be concerned about finding that replacement if needed.