Here is a great picture of the total Barracuda Formula S package. Check out the exhaust system and especially the resonator. From what I can see it's black! I found these pictures in the March issue of Hot Rod magazine from 1965.
WOuld it be possible that they did a mid-year change on the tip from black to stainless steel? I know the old President of the WPC Club also told me that the resonator tips were black.
