I think a couple of welded on lugs (onto the yoke tube) would be the best option, which the bracket/frame can bolt to. Preferably don't weld over the frame number!
The yoke could feasibly be drilled and tapped to bolt a bracket to it, but the tube is not really that thick. (And use short bolts that don't hit the inner stem and seize the steering!)
I prefer to have the capability to point the headlight beam in directions other than that the bike is pointing in, but that's just me
Looking at some of the bracket options on the web, it might be feasible to drill through the frame gusset behind the steering yoke tube to allow for mounting bolts. Probably the least "intrusive" option.