Installing ported heads, do I need a retune?

I currently have a stock cam, full bolt on LT1 with MadZ28 tune, and due to head gasket problem I am swapping out the heads for some ported heads and 1.7RR. My question is this, how bad will the ported heads throw off the way the car runs, as in too rich/lean, etc? If I get another tune will they need to know the flow numbers?

The MAF sensor should take care of the fueling issues, but you'll probably need to change the timing (most likely more advance across the board).