Well the problem with making a header for the 420a is that many people believe that there are minimal gains to be found. For example Greddy makes a header for the 420a, cost around $400 (i think), its a good quality header. SportCompactCar intalled this header on an eclipse and only got really low gains.

http://www.importtuner.com/tech/0202it_ppeclipse/index.html

Some members have installed headers on their cars and felt as though they wasted their money. Now I have a OBX header i got from SSautochrome for $135 shipped (if u email them they will cut you a deal even lower than ebay). As you know their warehouse is here in Morrisville NC. I live about 10 mins away in Raleigh, NC. I like my header, cant beat it for the price i got, and i got some nice gains with it. I do have cams, port work, etc so gains on my car would probably be more than a stock 420a.

I can come to the shop one weekend and let you look at my car for fitment or ideas, i even have a spare obx header w\o downpipe laying around somewhere (long story on why i have two).

What the 2gnt really needs is a custom intake manifold, with crane 16s my car needs more air flow.