The best method for chamber shaping and relieving, should involve placing the cylinder head onto the blocks deck surface, and then securing it with a couple of head bolts. Then flip the block upside down, and reaching down the cylinders, scribe the cylinders outline onto the heads deck surface. Once the head is removed, you can unshroud the chamber to this point around the valves as needed to further enhance its breathing. This method will guarantee that each chamber is unshrouded to each specific cylinder it will interact with regardless of any core shift in either the block or the head. Elongating the bolt holes wont allow the head to move, because it has dowels that locate it.
