I've looked into the IS3 cam before and i think with stock rockers you can get away with just stronger springs (130 or 140#) double roller and ported heads. I would be sure you have more than a quick port job though, because there is a lot of lift with the IS3.
Check this out.
http://www.3800pro.com/forum/cams-he...machining.html

and from here
http://www.grandprixforums.net/threa...a-Daily-Driver

Honestly man. Nitrous with your XP and call it a day