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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I swapped a set of these into my '68 when it was too loud.

Oddly the same e mufflers that were too loud on my '68 are much quieter on my '70. Both have TTI 3 inch full exhaust & headers, but the '70 is a 493" big block and the '68 a 408" stroked Magnum.

I also like to run ovalized megaphone tips on my cars, especially the electric cutout pipes. It improves the exhaust note much for the same reasons most wind instruments are designed with a flared end.

Super Turbo™ Mufflers - DynoMax® Performance Exhaust