It has been in the ford muscle parts manual since 1969 to machine .230" off all 1968 - 72 except CJ and .300' off all 1973 -95 heads I have been building big block fords since they were introduced and have never ruined a head yet . I have had problems with heads that some one never bothered to machine the bosses down . If you look in the back of the ford racing parts cataloge you will see that the specs are still there .