I do believe your theory. But from everything I've read, the chain adjuster is the difference. Does one adjust from the front and one from the clutch cover? I'll check when I go to the shop
Mine is a single bar stud with the adjuster on the side I believe. I don't recall seeing a 450 rancher when I bought mine 6 years ago. There was the 455 and the 460 rancher and those had adjustable oilers. I think there's a 465 now.