Of course another option is to make a new bolt head from scratch and correct the headspace that way, however if you have matching markings on the bolt head that you want to keep than the only way is to correct what you have. There is also a lot of work in making a bolt head and you will still need a jig to hold the bolt head as the desired thickness will need to be achieved using a surface grinder which will also make sure that the bolt face is parallel to the shoulder on the back of the head which contacts the bolt body.

Matt.