A chambered system is too restrictive? That doesn't seem to make sense. They were developed to be much less restrictive. Hence the noise issue.
Restriction and noise level attenuation are two different issues; the chambered exhaust system is both louder and more restrictive than the standard dual system, just as it was on the Corvettes of the era. Chambered exhaust on the Camaro and Chevelle and sidepipes on the Corvette used the same 1-7/8" I.D. pipes manufactured by Walker, and the option was driven by Marketing, not by Engineering.