1,2,3-4,5,6 is good for turbo manifolds and that is what I'll make for my Twin Scroll ERF 8474. 1,3,6-2,4,5 is "suppose to scavenge better. It would have been way easier to build if I built it 1,2,3-4,5,6. The header isn't perfect by any means, I have 1 tube 4" shorter than my planned 36" primary tube length, and my calc's showed it needed a tube size bigger than 1.5" but smaller than 1 5/8" Figured with the thought of adding my Vortec V1 I would error on the bigger side. I have to say, I was pretty darned excited when I test fit the header and it fit and cleared everything. the header goes in and out with the intake and passenger motor mount removed very easy. If I would have thought about it, I should have changed the layout of #6 tube so the header could have been used on high mount starter 200's as well. For those that don't know this is a 1981-83 low mount starter 200/3.3L block not a 250. I'll post pictures of the bell housing mod needed to use a SBF bell on this engine.
