How to quiet down my 3" exhaust?

My 68 Barracuda has full length, no crossover at all, dual 3" Dynomax crimped 3-pass turbo muffs, on the 400hp 367, with dual 3" over the axle tail pipes and turn downs.
The further the throttle valves are open, the louder it gets. At WOT and after 3500 she is a screamer. But people say from behind or on the sidewalk, it's a good scream. (well it's long anyway, because I use the GV as a splitter, and when she hits the rev-limiter, I just keep it there for 5 or 6 or sometimes 7 seconds,lol)
I have always had 3.55s (mostly), and in the beginning I had small tires, so it used to cruise at 65=3050(manual trans), which,long term, I found unacceptable. So I slowed down and cruised a few years at 56=2620, which was sorta doable,on my 20 minute commutes.
I then installed,some taller tires for 60=2560, but when those wore out,
I eventually installed a GVod, and 295/50-15s, and she now cruises very pleasantly at 65=2230; getting progressively louder with speed. But you know, a lot of that is wind-noise, as the ol' Plymouth bulldozes a hole in the atmosphere.

If I could do it over, I would put much smaller duals on it and cutouts, cuz daymn, those 3s are heavy. I think the pipes and muffs alone were 72lbs.