Do you know how much they're "off"?
Best solution (when it'll work) is just to enlarge the holes (#6 to #8) to get them correctly centered. This is commonly done on factory M700 receivers that are "off" from the factory, or magnums where many prefer #8 screws. Holes in the mount are correspondingly enlarged/counterbored for the larger screws.
If part of the existing hole would end up "outside" of the new oversize one, I solder a screw into the hole then grind it flush before drilling/tapping for the new ones. Welding is a bad idea for this application, a quick zap with a TIG or MIG torch won't affect receiver tempering- but if you've ever tried to drill and tap a tiny machine screw hole through a weld...
If you're absolutely certain the rear holes are correct the front ones could be installed in-line with them. If there's any doubt about that, I'd pull the barrel so the receiver can be correctly indicated with a mandrel through the bolt raceway. This is pretty basic stuff, if a "gunsmith" can't drill and tap holes for a scope correctly...
I'm in FL and backlogged several weeks, but feel free to PM me if you like.