Lots of mis-info on resonators.
They were used in production on dual exhaust Camaros starting on Day One, 1966. When Chevy had to quickly drop chambered exhaust as standard equipment on Z/28, L34 & L78 Camaros there weren't enough in the pipeline. So for a short time SOME cars were built with a single muffler only; some did get resonators. The under chassis photos of the 02D built #3 ZL-1 show it was built with them. By 05E all standard dual exhaust cars had them.
We did the #4 ZL-1 with a stock muffler/resonator system and it was very quiet.