How can I identify the displacement/year/etc. on an 85 horsepower Johnson outboard?

The seller doesn't know much about the boat. I could check the HIN on the Hull but I'm not even sure if this is the original motor or not. It says Johnson and 85 on it so I ume it's an 85 horsepower motor as Johnson motors do come in this exact horsepower. It's about the right size I'd expect an 85 horsepower engine to be. How can I go about trying to find out the specifics of the motor so I can order any parts I may need for my restoration project?