what size header to run

With so much passion and $$$$ put into that combo, YOU would be foolish to install a prefabbed header.

Get a "custom length header/collector" made, that matches the rest of the combo.

There is a program out there By Larry Mueax called PipeMax that will predict the exact length of primary tube as well as collector.

I thing its around $40, Larry is planning on releasing newer version this year.

The $40 one, has vary good information and will help predict induction lengths as well!