My 1981 glenfield model 60 (made by Marlin) has the alloy trigger guard. Not sure when they switched to plastic.
Do not dry fire a rimfire, it's very hard on the firing pin when it smacks into the edge of the receiver.
I remove the stock and trigger group to clean, thats it.
If you take the first two digits of the serial number and subtract from 2000 (or 2100), thats the year of manufacture. So mine has 19 as the first two, which makes it 1981.
Examples: 25 would be 1975, 05 would be 1995, 95 would be 2005 (since it's obviously not 100 years old)