Seems to me I use one of the existing stock holes and drill a new one for the other, which ever centers the pad so I can mark it for final grinding. Mine are on big bores, so I left the pads full for a bigger footprint, I only ground the mating surface and then tapered the pad sides a little to match.
Tim
This one is on my .405 Winchester...
http://img.photobucket.com/albums/v386/quickdtoo/405Win.jpg">
and the .45-70...
http://img.photobucket.com/albums/v386/quickdtoo/45-70.jpg">