1966 dart commando 4 speed id

My Aug 17th 1965 build date '66 Barracuda 273 4bbl. 4 speed came with an 8 3/4 and disc brakes. I've seen other 4bbl 4 speed cars that year with both 8 3/4 and 7 1/4 years. I also used to own 2 '66 Formula S's that were automatics and had 8 3/4's.