Yes Schwartz built the OEM loaders for MM, also Oliver, White & some Allis-Chalmers there were half a dozen or so different models, non are quick-tach, until you get into the White Years. All Schwartz are full frame loaders, that mount below engine & to rear-axles. They are not compatible with most cabs on these tractors, with a few exceptions.
Do NOT use the Light Schwartz for Round Bales, too light of a loader, also unless you have the I-Beam front axle, use any other loader with caution for round bales, you will likely Break the spindles & or front axle, these are not made that heavy (smaller bales OK, the big ones are much heavier). My M670 was used for round bales & I need a new front axle, busted, welded, not straight, etc.
Depending on your location, I have a Koyker quick attaching K5 loader with grapple for sale, cheap, if does need some hyd. cylinder work, as seals are leaking on dump cylinders. It is currently on an M670 Super. Located in South-Central MN