Like others have mentioned, buy it... now, before someone else does! I have the identical bike sitting on my lift right now in the process of restoration.
This R60 is the predecessor of the R60/2, which started production in 1960. There are a few notable differences between the bikes, like the aformantioned frame gusset. Check the centrestand mounts, as the earlier types were known to break. The battery tray is different, and so is the rubber strap. Good luck finding a replacement! The motor has a few differences also. I believe the con rods are of different design. The cam shaft gears are cut in the opposite direction and the metal gear is retained with a cir clip... something not found on the /2 motor. DO NOT attempt to pull off the gear and the camshaft bearing at the same time as the circlip is hidden in between them and you will damage the crankshaft... just ask me how i know
The /2 is considered by some to be a superior bike, but yours is more rare, and in my opinion, more desirable! Feel free to PM me if you have any questions regarding your bike. This is a picture of my last restoration, a '66 R60/2.