Your serial number indicates that your Marlin model 336 rifle was made in the year 1971.
1949. sales@countrygunsmith.net An F prefix was made in 1949.
That gun was most likely manufactured in 1979. Marlin firearms manufactured between 1946 and 1968 have a letter that precedes the serial number. Firearms manufactured between 1969 and 1972 are dated by the first two numbers in the serial number. i.e. 1969 firearms begin with 69, 1970 with 70, etc. After 1972 you must subtract the first two digits of the serial number from 100. In your case, the serial number begins with 21. 100 - 21 = 79. Or, 1979. You can get more details here: http://www.gundealersonline.com/firearmID_Marlin.asp
Marlin 1893 # 331272 manufactured 1906.
Your marlin model 1893 was made by marlin firearms in 1894.
14069
I would date your marlin model 92 to the year 1907.
Marlin Firearms is still in business. Check with them.(marlinfirearms.com)
Your marlin model 39A was made by the marlin firearms company in 1952.
The serial number plus the book on Marlin Firearms History by Brophy.
1958.
Early firearms in .22 caliber were not required to have a serial number. Your Marlin 81 falls into this time frame.
You can go to wikipedia and search under "marlin 30-30" the chart they have will show either a serial Letter/s before the numbers or if no letter or letters before the serial # then you take the first 2 numbers which are then to be subtracted from 100. ex: 25 - 100 = 75 (the year made.