This is not an uncommon issue with big block Cobra owners. You want your pipes at a level where you still enjoy the sound, it's clear that it's a nice performance big block, but you don't want a throbbing headache, nor do you want to have to wear ear plugs. I can't tell if
Stainless Specialties in Cleveland is still in business or not, because it looks like their web site has lapsed. But they used to build "quiet type" side pipes for several ERA owners, including me. Here's a thread on it:
ERA "quiet" pipes The pipes are absolutely wonderful and, if they're still in business (I think they are), I'm sure they could retrofit your existing pipes to make you happy. Their web site used to have a lot of good info, pics, and descriptions of the different baffling, sizes, etc. for side pipes. But now you're just going to have to call them up and chat with them.