If the new studs will not hold, rather than spot welding them why don't you put slightly larger studs in? There are probably a hundred different size studs out there. Maybe you can find one with larger diameter spline, or maybe even go to 1/2" NF thread. You may have to drill the hub and drum together, but you're only taking a little bit of material out. Just leave one or two old studs and nuts tightened, drill the other ones, then install new studs, tighten some nuts on the new studs to hold the hub and drum together, then remove the rest of the old studs and nuts and continue drilling out the remaining holes.