I have Thrush glasspacks on my coupe. They look and sound like the Cherry Bombs I used to get back in the '70's & '80's. At first I had 3 1/2 in pipes from the mufflers out the back , but the resonance was deafening at 40 mph and above. I chopped those off and put 2 1/4 inch pipes out the back. It still sounds fine outside, but not noisy inside any more.

I agree, Flowmasters just don't have the sound that works on a traditional hotrod. I like the sound of them, but on muscle cars & more modern stuff.