318 low budget heads change

.020 on block side and .019 on the intake side. it is about 1 cc per .005 milled off the block side. This should get you down to 68-69 cc on the largest chambers. This is for untouched heads. I said .020 since that is up to "no extra charge" for milling at my machinist. My numbers are for Chrysler small blocks taken from the Chysler racing manual. I have used these numbers for 30+ years and have never had a problem. The numbers are for every .010" removed from the block side remove .0095" from the intake side of the head. It takes .0048" to reduce chamber volume 1 cc. The chart you looked at was for big block heads.