1980 is too old to have LSHO. I had an '83 model 75 (same thing but short barreled) without LSHO.Look for a 1980 on down model 60, I prefer the Marlin/Glenfield for the pesky squirrel on stock.
Mine was VERY gummed up and even had a coating of yacht on the outside. Good thing because it cleaned up to look like new. I paid $100 for it about three years ago, no tax.I agree Waffletop, found one in a pawnshop a year or so ago and got a great deal on it. I could feel the grit as I manipulated the charging handle. So after careful inspection (noting all the crud in the upper receiver area), I purchased the rifle and got out of there as quickly as possible. After a good cleaning and a new buffer from Numrich, she functions like new! In my opinion, it's the best $ I've spent on a rifle...many hours of enjoyment at the range with my family.
It's not just the short tube the newer ones have, it's the short barrel. My 123456XX S/N gun is much quieter than a newer one.I do like the LSHO on my 1994. SO far the 15rd tube hasn't been a issue, I've only been attacked by 10 zombie squirrels at a time.