muflers today are not like the ones of years ago ,, back then I use to put on glasspacks (cherry bombs) and they cam in diffrent lenghts , longer was more quiter , at least until the packing inside burned out ,the older muffers had more baffles in them , your are right when the started using cats the didnot have to use much baffleing inside the muffers, I went through the same problem trying to make my pinto almost noise free, bad thing is I have a V-6 with headers , used a walker muffler , not to bad but not quite, tryed a NOS muffler (Midas brand ) corvair turbo muffler , that did the trick , now i can hear my radio , most muffler shops do not know anything about mufflers , they only have stock replacements or noisy replacments , the old guys knew how to make the noise go away ( short of sticking a water heater size truck muffler under your pinto , I do know some did have resinators ,