I found this on another forum, so I cannot take credit:
Fusil MAS 1936 (7.5x54mm) ... Serial number prefixes F, G, H, J, K, and L up to 45XX were all pre-war made. In 1945, the French restarted where they left off in June of 1940 ... L4600, the rest of the L series were manufactured in either 1945 or 1946. M, N, P, and Q were finished off by 1950. They then went to block letters: FG, FH, and FJ and so on until 1957.
What interests me is that your example looks to have been refurbished and reissued, as it has post-war parts, such as the front sight, magazine floor plate and sling swivel. One way to tell for sure what year is to take it apart and remove the wood - the years are usually stamped on the barrel, on or just after the breech. The wartime butt stock will also usually have a circular cartouche indicating the month and year of manufacture, though this often wears off with heavy use. You example looks to have seen rough times, but should still a fun shooter and great conversation piece. Have fun!