'81 is pretty close. If you do not find the number under the cowling, check for a small number plate on the tiller (port) side of the motor maybe 6-10 inches below the cowling.
If/When you find your model number you can put it in here to get a yr on it.
https://www.marineengine.com/parts/parts.php
I like how they have their site setup, makes hunting down an exact part easier.