Something odd looking about that bike. Maybe it's because it's a last-year model but the air cleaner and the front engine cover (with the bulge for the dampner) are R69S parts. The valve covers are R60 but the cylinders appear to be R50 cylinders. The R50 cylinders are flat on the front, the R60 cylinders have extended front and rear fins that form somewhat of a pointed shape. Perhaps that's the way they sold them in 1969 but still looks odd to me.
The advert certainly claims that it's absolutely stock and documents it through the original owner, so if it's NOT stock, that's a pretty egregious difference, especially at the price.
I'm not enough of a BMW guy to know which would be right and which wouldn't, though .....