Stone guy here. I mount sinks for a living. The pre drilled holes in the flange re 4" on center. If you found center of your sink to the right and left you should have 2 holes 4" apart from each other. There should be five holes in the sink all together all 1.375 - 1.5 inches in diameter. Drilling through the stainless can be done but it's not optimal. If you overheat the bit the steel will bruise and turn blue. You can drill a larger hole depending on the size of the escutcheon plate. What kind of material are you drilling?