I've got an '89 5.0 block .30 over, with Probe forged flat-tops with the double valve reliefs(for possible latter swap to tfs heads), and gt-40 heads off of an '93 cobra motor. I'm trying to approximate my compression ratio, but I've read many contradicting chamber specs., everything from 60cc to 65cc. What's the straight dope? I'd like a ratio in the middle 9 to 1 range. Do I need to have these heads milled? Does any one know what the chamber volume of these heads is? The engine is on the stand, so now is the time if I need to get them milled. Thanks.