How to quiet down my 3" exhaust?

I must be too old, because it's too loud. (More accurately, I prefer to speak softly and carry a big stick) :p

Anyhow, my 451 Dart has quite a rumble with headers, dual 3" with X-pipe and full tailpipes, Summit "turbo" mufflers in the stock locations, and glasspacks under the trunk floor for resonators. The tailpipes are just turn-downs stuck in the ends of the glasspacks, but come out the rear.

There is a fuel cell in the trunk, so plenty of room for additional mufflers under the trunk.Will replacing the glasspacks with another pair of mufflers help? I want to re-do as little of the piping as possible.
I could put long-case oval Walker mufflers under there.

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