Jan's Shorty Header (with a Vibrant GESI high flow cat) and the Milltek are the top line header units. With allot of folks now buying used Gen1s there may be some new interest in headers and high flows with many Cat makers of today not being around back when the Gen1s came out. The Asian headers are cheap and although there will be those that say they are crap, there will always be somebody out there that will buy one. On the cats, the rule is thumb is the cheaper the price, the less precious metals to act as catalyst agents and that many will not hold up under the forced induction heat/pressures that the S produces. The other issue is the space where the cat can be installed. The factory cat is about 5.25 inches. There are allot of high flow cats out there but longevity can be linked to the overall diameter and a number thrown around is 130 mm (5.1") but most of the "green" highflows are 6" in diameter so unless they are very short they will be hitting the heat shield on the back end of the unit. Kooks is in NC and makes a green cat that they say is rated for 900 hp and the high temps of a forced induction car. Its not cheap and is the "magic" 130 mm in diameter but at 12" long it may top out towards the back. I am thinking the tunnel tapers down about 4" in front of the cat back exhaust flange that coincides with where the factory cat stops. Thinking it is a 300 cell unit. Something less in cost then the Kooks green cat is a Pypes CVM11k that is made for a Mustang that they say is rated for forced induction, the problem is they do not sell a single 2.5" cat but rather it is double as the Mustang has two pipes. I have had some discussions with them and told them their cat looks promising as the size would appear to work quite well for an OBX type header. I did not get into the metallic matrix folding with them (see below). It appears that the metallic matrix holds up better with the higher egt's of our superchargers. Just as the 130 mm diameter appears to be important the manner in which the metallic matrix is folded/wrapped also makes a difference. The simple paper towel type wrap (start in the center and wrap outwards) is the least expensive with an "S" type fold being better. Yonaka uses the "S" wrap but is an inexpensive high flow cat.