For the folks running lower-rpm, higher displacement naturally aspirated engines (say, 400 cubic inch and above), what have been your strategy to get reasonably quiet exhaust that isn't too restrictive? I stumbled across Flowmaster's purportedly quietest series of mufflers: https://www.flowmastermufflers.com/products/exhaust/mufflers/street_chambered_mufflers/50_series_big_block/ . These would, coincidently, go behind a big block (Chevy). Muffler size isn't an issue, since my fuel tank is removed (S30) and there's a fuel cell in the hatchback area.
My question is about simultaneously quieting the exhaust and keeping backpressure to a minimum. This would be dual exhaust, of course, with a conventional crossover pipe, and headers (for the moment, block huggers).