That big rectangular plate on a transmission is a pretty much standard PTO access regardless of the manufacturer. All sorts of PTO's can be adapted to that opening- - -single speed and direction, reversible, and a few other options depending on the intended purpose. A SM 420 has a non-synchronized granny gear and a direct drive 4th. gear- - - -good technology from the late 1940's, but a little obsolete these days. Rock crawlers love them because they're rugged and low geared. I'd much rather have 5 or 6 synchronized gears, given a choice between the 420 and something 50 years newer, particulartly where the availability of repair parts is concerned,
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!