Chris, when You use the plastiguage, if the engine is upright when You check the mains, use a jack and a block of wood to push the crank up against the block bearings [lightly] to be sure You get an acurate reading. Allso, the crank MUST NOT rotate while You are checking it. The bearing shells will be marked if they are for a reground crank. Plastiguage is the easy way to check an engine without tearing it all apart, it is cheap & easy. There are different colors for different clearance ranges, I forget what they are.