If this helps, my '84 had stock exhaust manifolds, x-pipe (no cat) and 2.5" pipes back to some stock LT1 mufflers (this is how the car was equipped when I bought it) when I began my muffler quest. I wanted a little more "rumble" so I replaced the LT1s with Flowmaster Super 40s. They sounded great from outside the car (a lot of compliments from others), but really resonated inside the car. I tried installing sound deadening, but that only helped a little.
I then replaced the Flowmasters with Magnaflow mufflers. I'm very happy with this arrangement as it is more throaty than the LT1a, but not as loud on the insed as the Flowmasters.
I know many folks will weigh in with suggestions for Corsa or Borla mufflers, but I was looking for a good sound with minimal expense.