I was given an old trainer plane with an OS engine. This engine is a plain bearing 30. It has raised letters on the case "MAX-S OS". The back plate has serial number 3007 (or maybe this is the model number). The crankcase has a 3001 and "AK" stamped below the mounting lug. Can you tell me how old this engine is?

It is in excellent condition, maybe only ran a couple of times.

thanks, Lem