What came with my TTI 67 Barracuda 2.5" dual exhaust kit were a pair of Dynomax Super Turbos, part # 17733. That muffler's overall length is 18.5 inches, and it has an offset inlet, center outlet. You would of course need only one. There are other sources, but Summit Racing has that muffler for $55.99.
Dynomax Super Turbo Mufflers 17733
B bodies use a longer muffler.
