Why why why limit yourself with stock heads? The combustion chamber is a joke.
Talk to Brian at IMM, OU812 on this board. Seriously, there is a better way than using the crappy stock combustion chamber. Of course it can be made to work, but the Mag head chamber is better, enough so that it's worth pursuing. The EQ iron heads with the Mag chamber are one way.

But, even if you decide to saddle yourself with the stock heads, those 720 gram stock pistons have to go.

R.