There was a lot of discussion a week ago in this thread
http://67-72chevytrucks.com/vboard/s...d.php?t=506642. Lots of different opinions. I'm also trying to decide on 2-1/4" or 2-1/2" dual system. Just remember all these trucks with small blocks had single exhaust systems. I think the original diameter was 2-1/4" (not 100% sure). So, even a dual 2-1/4" system is a lot of flow compared to the original.