Formula S.... Is a suspension upgrade package from the standard suspension, bascially bigger t bars, bigger springs, bigger shocks, and most came with a 340 or a 383 under the hood. Also the grills where different, the inside ring should be black or argent, trying to remember which one was for a formula s, and which one wasn't. If you need more info, contact me, I got a 69 340-S and a 68 383-S