I used to have a 1987 yellow vert too. They didn't make that many of them. I really loved that car, wish I could find it so I could buy it back.
On mine, I had the 'monza' mufflers from MidAmerica (not much more than eliminators), basically, they are glass packs. little to no resonance, but they have a hell of a growl... The do get louder over time however resonance was never a problem.
My Dad had the same monza mufflers on his '87 coupe and '91 convertible without resonance. he currently has the mid america power curve exhaust on his '98 pace car and they have horrible resonance so I know the difference
I have a 90 convert and I replaced my mufflers with 3 in stainless pipe. Isn't a good idea if you want to be able to talk to your passanger. I found that the exhaust noise came over the back inside. I wouldn't say there was a
resonance but it was loud. Would be ok if you don't drive over about 25 miles at one time,not good for long trips. Course there are always ear plugs.
I have the M-A elims on my 87 coupe and I really don't have any resonance. They do sound nice, but the stainless LT1-stype "tips" have an annoying buzz to them as a pinch weld has broken loose.
As far as "passing inspection", they are mufflers and have nothing to do with emissions so unless you have a state minimum noise requirement for vehicle inspection, they will work.
But if you want a louder car and not a lot of resonance, just get a muffler shop to remove the factory mufflers and have them add a piece of open pipe in their place. Great sound and probably won't cost much more that $75 including a set of tips.
Warren, how are you , I was just thinking about you. Yea, I sold the 99, I don't drive them that much, and had a few repairs that run over 4K. Since I'm retired, I use my money elsewere. I bought this yellow 87 vert. I can work on it myself , for the most part, and ins. is only $230. a year. Serves my purpose, but I could get in and out of the C5 much easier. Still kicking and having fun, Jim.