For the '69 Z/28, they began using resonators in mid-April. At the same time. they began using chrome tailpipes. Gardner Exhaust makes a very nice complete exhaust system with the resonators and chrome tailpipes.
The recall notice Chevy issued has created much confusion.
First of all resonators were used on some dual exhaust Camaros at the start of production August 1966. When the Z/28 was introduced one of its' features was "deep-tone dual exhaust" meaning no resonators. Deep-tone became an option; exhaust systems were unchanged through the '68 model year.
For '69 Chevy included the noisy & restrictive "chambered" exhaust [NC8] for Z/28, 350 & 375 hp 396 Camaro SS. Camaro SS with 350 and 325/396 continued to receieve the standard system with resonators. Within a few months of the model year owners of Camaros with NC8 were being ticketed for excessive noise and Chevy had to replace the systems. At the time there was not nearly enough resonators available to retrofit all the cars in the field-some got them, some did not. The recall notice states that recalled cars that initially did not get resonators could be later returned again. The same was true in production for that time period-some got'em, some did not. Original underchassis photos of ZL-1 #3 built 02D shows it was built with the single muffler/dual resonator system. By about April all dual exhaust Camaros not ordered with NC8 had resonators.
Chevy Central Office issued a letter May 19 stating that chrome tailpipes would now be standard equipment and NC8 was dropped as an option. All cars with dual exhaust as standard equipment had a slight price increase as a result making it simple to pinpoint when it occurred. Cars built in April do not show the increased price.
At that time all dual exhaust Camaros had the single muffler/dual resonator system with chrome tailpipes as there was no other system available.