All YS 1.20's were marked on the crank case as F-120. There were several different models of the 1.20 made. The only one I am positive yours is not is the AC because it does not have the air chamber between the carb and the head. Other than that, it could be anywhere from 2 to 11 years old. Yes, they are strong running engines. When each different revision of the engine came out, it was the most powerful production 1.20 you could buy. Even the very early 1.20's would be considered high end sport engines today.

John