1964-65 Barracuda question

Thanks Cuda, I couldn't find any designation to the Fomula S package on the serial number. Only in 1966 it shows a high performance 273. Actually my friend is looking at car to buy. He says its in nice condition in and out. I'm just trying to get him some facts on the early A Barracudas. Would you know what rear the car would have had if it were a Fomula S car? Thanks Mike