I agree with James's suggestion. He should probably be thought of as a national treasure.
I do have one caveat, not all screw slots have parallel sides some are tapered. I've seen this on more than one high end German gun. I have a theory on how this was done but I'm not for sure so I'll keep my thoughts to my self. My point is don't assume anything. I've modified a few old wood handled Grace screwdrivers just for that purpose. BTW, I love wood handles they just feel better than plastic.
One other passing thought on screw slots, CJO and I were perusing the fine shotguns at the Southern a few years back and he said "look at this!" a Rizzini R1 (I think) had the narrowest screw slots I've ever seen. I have no idea how they assembled the gun tightened and timed the screws!
