Hey Andy:
I have a manual from "Headers by Ed". He says that the primaries should lay out in rotation of firing order. Clockwise or counterclockwise isn't critical. But it should go 1-3-5-7 and 8-4-6-2. Standard cam firing order. That's not how the drivers side header is set up. But I have seen the pattern on the Chevy motor before on other headers. Is it just ease of fitment, or another theory on what works best?