They don't have clips. They have magazines. You can order them through Numrich.
older because is your tube fed long or short then the barrel mine comes to the top new are short.Your serial number indicates that your Glenfield model 60 was made in the year 1981.
ammoclip.com $18 plus shipping The Glenfield model 25 was made by Marlin as the model 80
yes 1970 is really not old for this rifle they have been making it for one hundred years they switched to smokeless powder around 1910 hasn't changed since. the new rounds still follow same pressure specs.
Yes, there is a kit available which fits Marlin Lever action rimfires from 1891 thru 1939.