Indeed, not a lot of change over the decades. Some rifles clearly have an obviously older stock as revealed by it's shape, especially the butt stock, but it doesn't necessarily mean the barreled action was original to the stock. As you note the front globe sight has changed over time, from dovetailed varieties to a more fixed, pressed fit globe on rifles with a higher serial number. Other differences include the front barrel lug changes over time, left or right side extractor as noted above, visible pinning of the barrel to the receiver, as well as the bolt handle recess in the stock itself.
It would be a challenge to offer any assurance whether a rifle that looks like a M70 or M77 is one or the other -- or something else all together -- as so many of them come to Canada as hybrids made up of parts from several different original rifles. We can tell from serial numbers on the rifle what model they likely were when they began their life, but decades later it can be hard to tell.
I'm glad you enjoy the S&L !
