If you're not going to increase the bore size, I don't see why you would need to have the pistons "cut to match" the head. I don't think aftermarket 84mm pistons will need to be modified to work with a stock B20 head. If anything, while you're getting the head ported, you can have the cylinders deshrouded if you think you're not going to have enough clearance for the higher comp pistons.