Biggest mistake people make is to try and re invent the wheel.
You would struggle to skim the head enough to compensate for the dish, and end up with anything above 10:1
Plus you would have brought the valves 2-3mm closer to the pistons thus requiring cut-outs (because your gonna use a performance cam right).....so you may as well use decent pistons from day one.
Plus the dish is a device to create a slower burn for emission's purposes.
Oh and you would have screwed up a perfectly good head will end up with an underperforming mongrel