They do require a much finer surface finish on both the head and block or they will not seal as intended. And both the block and head have to be machined, its not an either/or option. This is also something that not all machine shops can perform that has older outdated equipment, so it may make you have to travel farther outside your area to find a shop that is qualified to do it. Adding to the cost of your budget also. But it is money well spent.
