Savage owner asked Big River Guns the same question.

"....a standard Savage 110 Left hand version. In 1969 Savage started the letter prefix system and the last serial stamped in 1968 before this change was 129000. According to the records your gun is a correct left handed 110 in .264 win mag made in late 1965." Big River Guns, Muscatine, Iowa





Read the footnotes at the bottom of the page where L and M prefixes are discussed.

https://www.savageshooters.com/content.php?263-Savage-110-Firearm-Dating