Are you sure they are Dynomax? I haven't got my car on the road yet but I ran the engine with those mufflers and manifolds on a test stand and its pretty tame. From the TTI website:
Mufflers: 67-76 A-body exhaust systems were designed using the
Dynomax Super Turbo mufflers. Our personal preference due to the mild sound level, true performance tone, and minimal interior resonation noise compared to other mufflers.