While the 6.0L block typically retains its factory trueness, the same can’t always be said for the cylinder heads. They’re notorious for warping and cracking—and once the cracks protrude into the valve seats its game over (you’re buying $3,000 worth of heads). This is why it’s so important to have your heads resurfaced and magnafluxed by a reputable machine shop. The heads’ maximum allowable difference in flatness can be no more than 0.004-inches across the total surface area. Like the block, our heads checked out OK.