Did not have to mill head. However, I heard a rumor that the drilled/tapped holes in the block were not deep enough to accomodate the bolts if they stretch even a little. Have also heard that the bolts have some natural tension which they give up the first time they are removed. Suggest that you do search on site for the brand of gasket you have. I believe there is a post out there which says which gasket version is the best. I don't know if there is any definite info about the sealant that seems to work best but I bet if you put out a specific querry, some of the regulars will give you the info.