Originally Posted by MARTINSR
Making the tap tighter can help a lot too. Make the new part bigger than the hole, then set the new part on top and scribe around the edge with a sharp awl. Grind (or trim with snips, depending on how much you are going and the part involved) the metal out to the scribe line and you then have a near flawless butt to weld. Sure is nice to see beautiful work like that repairing an original hood instead of sticking some Chinese junk on there.
Good advice and we all know how hard it is to find a flawless butt.