As you can see, it started a bit rough, and I got a little close to the stud holes. I ended up adding just a little material with alumiweld, and it will seal just fine. Went way faster than the drum sander method, and once you get it started it goes very quickly. Actual drilling time was just 2-3 minutes with stops included to clear chips and add lube. I'll still need to go in there with the dremel and carbides to clean up.