Magnum replacement heads

The real question is can a hack like myself, make something decent out of them. That's why I do appreciate any input or advice on them. I do have the ability to machine them, just not 100% sure what all needs done. Guide size seems to be 8mm on these, and his old magnum OEM castings have .312 stems in guides that are just about .314. I thought all magnums were 8mm?