putting a big block with the new dart heads in my 66 Chevelle Car is original 138 so has the big block mounts. These dart heads have the exhaust port raised 0.300" so I'm told there are some header issues. Tried both Hooker and Kooks, but both say they don't build a header for this head in the 66 yet. Talked with with Lemons and they can build me a header but if I go with the 2-1/4" primary they will have two pipes over the frame keeping my front tire width to a max of 5". Motor is a 582 Dart block /Dart Head and power is dynoed with the 2-1/4". Haven't asked the design folks how much I'll lose if I go to the 2-1/8", but will have to if I stay inside the frame.
Anybody build this combo before...got any ideas as to what will work of if any of the off the shelf headers will work.

Thanks