Found this info about a Chevelle
The 1970 -72 Chevelle Model year dual exhaust systems consisted of 2 1/2" head pipes and 2" tail pipes. The small blocks accomplished this by reducing the head pipes down to 2" at the manifolds. Both the big blocks and the small blocks had 2" tail pipes with resonators but each resonator was quite different. The small blocks had a 2" tip with an angle cut in it. All of the big block cars from 1970 -1972 had a dome shaped resonator which ended at 2 1/2" allowing for the chrome tip. Our reproducion exhaust kit comes 14 ga aluminized with correct 2 1/2" head pipes with wrinkles and flats, correct extensions, donuts, flanges, mufflers, 2" tail pipes with correct resonators welded on, correct GM style clamps, installation instructions, diagrams and sealant. Our exclusive reproducion hangers are available with this system, as well as correct GM heat riser and stainless steel stud kit with correct lock nuts. Ask about our concours show pkg. for those who like it just a little bit better than original.
Here:
Gardner Exhaust
I would love to have one of their systems on my small block.
Bruce