I dabble....haha. Too many engineering classes I guess.... About the exhaust- If you have your port timing where you want it and have it blended through to the exit and polished somewhat you should be fine. I dont think increasing that inside diameter is going to net you alot of numbers, if anything it will reduce exhaust flow velocity and take away some bottom and mid rpm power. Also you wont gain anything if the I.D. of the exhaust port is significantly larger than the I.D. of your expansion chamber inlet. (more turbulence, less flow, less power)
EDIT: theres some cpi pipes in the for sale forum that popped up today, better hurry!