Quiet muffler choices

I have gotten to the point of building the exhaust system for my '67 fb Barracuda. It has a 372/340 with a 833 trans. For exhaust I have Doug's headers, Summit 2.5" X-pipe kit and Flowmaster 15826 tailpipes. My problem trying to find flow numbers for the Walker Quiet Flow mufflers 21548 and 21856. The other mufflers I am considering are the Dynomax Super Turbo mufflers 17749 and 17662 which both flow 700 SCFM. From what I have read on on FABO and else ware the Quiet Flows are quieter but reduce to 1 7/8" internally which means the are not going to flow as much as the Super Turbos. My question is how much do they flow? A number of people recommend the Quiet Flows including VOETOM because they are quieter then the Super Turbos. I just want to do things right the first time. Thanks