I must agree with blackfoot, either get an aftermarket one, or don't touch yours (for lightenning purposes).
I've heard that on most Porsches from the 80s, the flywheels have a special surface structure to them, when machined the clutches can't grap to well. I don't know if there's much truth to this.
I would think that if you take enough weight off the standard flywheel, you might give up some of it's structural integrity.
PS: Most sport/aftermarket clutches are 2-8 lbs lighter than stock
Ahmet
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It's all the driver...