Look at the thickness of the head casting where it meets the block below the spark plugs. An unmilled head will be approximately 1/4" thick there. If it's been milled enough to disrupt the head/intake fit and compromise the bottom of the intake ports, the thickness will be closer to 1/8". When I would angle mill heads 0.100" to turn a 76 CC combustiom chamber head into 60CC's, we also had to custom fit the intake to the heads to make the intake ports line up. Ray Charles could have caught my milled heads by simply running his fingers along the sides, but the tech inspectors were too dumb to do anything other than check casting numbers. If a head is milled straight down instead of angled toward the spark plug side, it only takes about 1/16" of head nilling (.0625") to start running into intake runner problems. Once heads are milled very far, the heads and a custom fitted intake need sto stay together as a matched set.
Jerry
