1965 barracuda commando 4spd.

Not a Formula S
In the alphabet row, it would need to have the number 2 under the letter C.

The 31 under the AB does signify a 273-4 barrel.

Check out this document:
http://www.earlycuda.org/techdocs/6265FenderTagDecode.pdf

Some fender tags may have an S shaped hole punched in them. This is an inspection punch stamp. It has no meaning other than an inspector at that factory did his or her job and inspected the car that day.