On my model 20 its on the left side of the barrel directly up from the clip.
your marlin/glenfield was made in 1974.
With the serial number that you have supplied,your Marlin(Glenfield) rifle was made in the year 1980.
Your Glenfield model 60 was produced in 1989.
With the serial number that you have supplied,your Glenfield rifle was made in the year 1973.
1975
1975
1979.
Your Glenfield model 25 was made in the year 1988.
Your serial number indicates that your Glenfield model 25 was made in the year 1976.
To determine the age of a Glenfield Model 25 rifle, you can check the serial number, which is typically located on the receiver. Glenfield, a brand associated with Marlin Firearms, produced these rifles from the 1960s to the early 1980s. By referencing Marlin's production records or contacting Marlin directly, you can often get an approximate year of manufacture based on the serial number. Additionally, examining features and design elements may help narrow down its production period.
The AB prefix to your serial number indicates that your glenfield was made by the marlin firearms company in 1966.
With the serial number that you supplied,your Glenfield model 60 rifle was made in the year 1978.