65 Barracuda exhaust

I haven't seen a factory dual exhaust on an A-body prior to the 67 MY. The reason they didn't do this is because the TB cross member is designed to clear the pipes only on the drivers' side. The 66 and earlier A-body cars I've seen with duals either had the PAX side routed over to the clearance area and back across under the transmission or had the pipe routed under the TB cross member on the PAX side. All who I have spoken to about the under X-member installation have reported that the pax side pipe is vulnerable and had either been flatened or ripped off.

As for the single system, my experience is that there were two different mufflers used. The 65 273-4 used a straight through muffler similar to a Dynomax Ultra-Flo, the later cars used a low restriction reverse flow muffler not unlike a generic "Turbo". The 65s sounded sweet, but were loud. IMO, that's why Mopar toned it down. My 66 GT had the reverse flow muffler. Had I kept the car, I would have put in the Dynomax.