Looking forward to seeing the picture, but the thing you are mistaking as a resonator is really a cat. The thing you are mistaking as a cat is a pre-heater. Both are required emissions components. Since emissions are required, a muffler shop won't touch them, and only removing them completely would help with your sound.
Replacing them with a high-flow h-pipe is probably your only option. You'll get better flow and better sound.
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351W 89 Mustang GT Convertible