[William]

The only difference between sb chambered and bb are the manifold pipes.

HRM did a great exhaust tech article a few years ago. The car used was modified '70 442. I recall the system that ended up at no power loss was 3" with an X pipe. X is supposed to be better than H.

Many years back one of the Illinois crowd told me his '69 Z/28 had more power on the chassis dyno after he replaced the OE chambered system with the standard transverse muffler.