The parts diagram listed that muffler for the single outlet L6 engine exhaust. The V8s had the dual outlet in the late '70s, so maybe they just don't carry the L6 muffler in favor of the V8 muffler.
I can ask my shop on the Z28 parts, but I'm pretty sure a single 2.5" exhaust is cheaper then getting fancy with faux 2.25" dual exhaust in the back. Actually I think the $200 quote was based on his confusion at thinking I had a V8 and he was putting together a dual exhaust, so I think that was on the high side.
I'm the one who pointed out the 2.25" outlet for the integrated 1bbl 250 head was located between cylinders 4 and 5, which is about the same spot as the 2.5" HD outlet for the non-integrated 2bbl 292 head. And they both have a three stud bracket. So an exhaust set up for the integrated 250 should be pretty close to hooking up to 292 manifold in a top end swap to a non-integraded head and manifold. The 250 1bbl non-integraded 2" exhaust outlet is located directly below the carb and has a 2 stud flange.
