Looks like it also is a 4 speed code.
Check out this site.
http://www.chevellestuff.com/
Click on 1967 and then on the dropdown Chevelle, then on the next page click on 1967 Chevelle Information. After that you will see different clickable buttons across the page go to <font color="red">Information - R to Z </font> and then down to Trim tags. He has several trim tag pictures with them decoded. Seems the "L" was for the M20 tranny. Have fun, lots of info on his site.