1968FormulaS340 said

Im just posting what Plymouths own sales literature from 1966 says.

It specifically says that a Tach is standard on the 66 Formula S, here:
http://www.hamtramck-historical.com...ershipsPlymouthOrderingInfo.shtml?load_img=55

And here:
http://www.hamtramck-historical.com/images/dealerships/DealershipDataBook/1966/66_Barracuda_0008.jpg

Click to expand...