The 1965 273 Commando (Plymouth) engine package consisted of a four barrel Carter carburetor, a slightly hotter 248 degree intake/248 degree exhaust/28 degree overlap solid lifter camshaft, 10.5 to 1 compression domed pistons, a dual point distributor, black crackle valve covers, and a chrome oil cap and air filter housing. The package's special single exhaust system consisted of a bigger Y-pipe, a "straight-through" muffler, and a black resonator with a square tip. (The tip was changed to stainless in 1966, and the straight-through muffler was replaced with a reverse-flow in a effort to quiet down the exhaust note, which was quite loud on the 65's. Lots of tickets were given for loud mufflers on '65 Barracudas and Darts. The usual excuse was "But, Officer,it came that way from the factory!" It didn't help. Note that this engine and exhaust was available without the Forumla S suspension package in 1965, on Valiants and Barracudas..it was called the Rallye package and apparently (despite dealer order books to the contrary)could be purchased with a three speed column shifted transmission. I've seen only one (a Valiant Signet two door hardtop) equipped this way. With this engine, you got a "Commando V8" emblem on the front fender of the Valiants and Barracudas, just behind the headlight. Dodge Darts got a "273 Four Barrel" emblem, mounted on the front fender between the wheel housing and the door opening, about 4 inches below the top of the fender line.
Even after all these years, I've never heard an factory exhaust sound quite the same way these did when they first came out in '65. I tried to duplicate it on my own '65 Barracuda many years ago, using what factory parts I could find, but it was "only close"