Go to the bottom of the forum main page and you will see the reference library. There you will see Hi-Lo Owners Manual and click on that. You will find a 1981 manual list part way down the first page. Click on that and you will see hilo1981.pdf. Click on it. That is as close as you are going to get, but the Hi-Lo manuals are not model specific and a year one way or another doesn't make much difference.
I would give you the link to go straight to it but is good for you to learn how to explore the website. There is a ton of information contained there. Always check the logon main page first and surf all the subject categories.