As a matter of fact, no Formula S was factory equipped with an 8 3/4 as standard equipment until the 340 came out in 68! It was an option starting in late 65, so Joel is partially correct!!
And a note to the OP, take a pair of calipers with you and measure those torsion bars, not an easy or even thought about swap!! If they don't read .870, they're not the big bars and probably not formula S!!
