I had the same generic glaspaks put on my Suburban as I had installed on the '56 with a 350. I love the sound of the '56 but on the burb they were too loud, as you describe. I added a pair of
Walker mufflers near the outlet of the pipes and I love the sound.
My theory is the long section of pipe after the first set allowed the noise build up. I'd suggest putting what ever you use near the end of the run.
