if that was the case i would def go with the cosworth, it is a hell of a piece man, look at the testing they did on it,
Just ebay search cosworth headgasket, and there was only one seller selling them, he is out of Cali, they make several sizes and thicknesses. i went with the 87mm bore 1.1mm thick on my stock bore build, the gaskets is soo nice. You will get the sealing you need from that thing, you might rethink the arp's especially if your using the old style. I would ditch them and go with new stock headbolts. They hold up way better, ive never popped a headgasket when i was boosted. Ive used cometic and cosworth and the cosworth is by far the best one.
Again just ebay it, there was only one seller, he will just ask you what size you want which you need to include when you pay for it. he is very fast at shipping, Again awesome piece for a great price
Here is the link.
eBay Motors: COSWORTH METAL HEAD GASKET S13 S14 S15 180SX SR20DET (item 370092885678 end time Oct-06-08 22:05:23 PDT)