Replaced the 750 carb from one 454 to another, went from a DP to a VA.
Started the car and it would hardly run and it sounded like open headers. Checked the float level etc and the engine under hood sounds fine, but barely runs. I think it was coincidence that the sound was so loud and probably has nothing to do with the carb changing as it was fine on the 69 right next to my other 69 with the same engine! I checked for exhaust leaks and see none, however the left pipe was blowing junks of rusted metal and what appears to be carbon. I had these used Dynomax super turbos installed about 50 miles ago. I am thinking the one muffler is clogged up preventing the the exhaust to flow properly or installed backwards. Hope I can get the car to the exhaust shop if that is the issue. What are your thoughts.

Not sure if super turbos are reversible but, Looking at the internal view doesn't look like it would cause too much trouble.

The car runs fine with the Mechanical secondary? just not the Vacuum secondary. Did the car with the vacuum secondary run ok?

Symptoms could be a blown power valve in the VA carb.
I wouldn't worry about exhaust, exhaust is exhaust.
Might put back on the DP and compare results.

The carb just came off a running driving 454 and installed on the same engine, different car. If this was not the case I would agree with your diagnosis. The sound and crap that came out of these old mufflers is what is strange in that if the muffler is shot, it would not affect the running of the car unless it is clogged up and the engine is not exhausting any??????

Pop them mufflers off and see how she runs.