As always it depends. He might have to take upwards of .005" off. Any more than that and you wouldn't be shooting 1.5MOA. And also depends how close to min spec the shoulders are right now. If its near max spec, you bet ya, its going to have to be reheadspaced if he has to take off too much material. But probably, he won't and probably the headspace is in the middle of the range. He can tell you some of this before he starts work with go and no go gauges with spacers and might even be able to give a rough estimate of how even the lugs are now. Lapping the lugs from what I have seen (I haven't performed this myself) is usually polishing and getting that extra .001" of evenness.