How to quiet down my 3" exhaust?

I definitely want to keep it free-flowing (the 451 is probably near 500 hp at the moment, and quite a bit more when I put the massaged aluminum heads on this winter that flow 293.5 cfm).
There is room for almost any muffler under the trunk...
Doesn't Flowmaster have a 70 series too?

You corrected me. That's the one. It's crazy long. But it will quiet you down. With you making more power upgrades, tread lightly on the idea of making it quieter. It will be interesting to see what others have to say about the matter....

JW