That is a great looking machine for it's age, looks to be well taken care of.
Here is my dad's he bought new in '76, by far the best piece of machinery he ever had, got it in my possession now.
I too will second that this is a great engine. My dad and sister ran it low on oil back in
'92 I think, snapped the rod. We replaced rod and rings and back in business, still running today. We used to till all summer, throw back in barn, then come spring, it would fire up on second pull even with old gas, never had failed to start. It is beginning to show some age though, engine is getting blow by after some working and needs carb rebuilt. and I don't have any muffler anymore, rusted out and yes, it's loud. I just replace axle seals, the old ones come out will punch or screwdriver, then just gingerly tap the new ones in place.
I have two part numbers for those, can't remember which ones the local shop used.
921-04031 or GW-9609.
I even use it in the winter for snow removal.