On my '67, that is the location of one of the "secret" partial VIN's. Mine matches the numbers on my door frame ('67 VIN tag). I'm thinking that matching issue would be the same for all FGF's.
How close is that number to your actual VIN number? Some people have reported secret VIN's that are off a digit or two. All the stamping back then was done manually so there were some slip ups.
I am hoping that your other documents at least agree with that your car was built at Van Nuys (the first "L" in that number). Another potential issue is that the first digit past the "L" being a "1" suggests that your OHC car started life as a V8 body shell according to the 1969 VIN info on this site (L6 cars started with a "6")
Otherwise, you may be looking at some hanky panky involving your car's VIN number in the past and that may not be a good thing.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
