Formula "S" question

'66 model has a "7" under the "F" for formula S.
All had tachs in the dash. 10's, front stab bar, 5 leaf rear springs (i think) 4bbl commando motor, 64-65's had a letter code under the "C" and it should be a "2" for "S" package.


I have seen a rear stab bar on a non "S", and tachs and stripes and 4bbls. Not hard to clone with options. Can anyone tell me what the difference is between the non S torsion bars?