For me, it really depends on how they are going to be re-attached to the quarters. If plug welded, just drill them out and you have a nice hole to access the new wheelhouse metal. If spot welded, a special sheetmetal bit drilled from the wheelhouse side would be your best bet, but be careful with the depth you drill with those, I've had significant (read; deep) scoring on the "good" metal if I wiggled on the drill to much. In addition, you will need a 90 deg head on the drill to do this properly, as there's just not enough room in there for a conventional. Some guys split it apart with a chisel, but the potential for damage to the quarter is too great IMHO. Just go slowly and you should be fine, whichever method you choose to go. Good luck