The stock CDI system on your car is hard to beat. With everything you are doing, you at least need to change the ignition system. The ability to map the spark is the biggest weak link you have on your CIS car right now (yes, EFI is better, but CIS is still very respectable).
Goran is right about the C2 cams to 8k, unless you retard the hell out of the cam timing. If so, don't look for boost anytime soon... By the way, what turbo are you going to use?
As for twin plugging, your displacement is at a point to seriously consider it - 3.5L. Anything above that is required due to the speed of the flame front for this displacement and effective compression ratio (higher CR = harder to light the flame). At your point in this build, the adivce to go ahead and put the additional holes in your heads is good. Your stock CDI system will be ample to drive a nice hot spark in a single plug configuration if you choose. Again, the main problem is mapping the timing to the MAP and RPM.
To do this right (looks like that's what you are doing - building the worlds most powerful CIS car
), you are going to need to spend more money on a good iginition system.