I pulled mine to be easier to work on and to replace all the seals. All the covers- front, rear and oil pan are designed to work in concert with each other. Alignment is crucial and there are specs for it. Install the front and rear covers first focusing on being centered to the crankshaft. But, they also have to be "clocked" properly. Meaning, centered on the crank but not rotated any so that one side of the bottom edge is below the block skirt and the other side high. Otherwise, when you tighten the pan to the block, it'll hit that point of the cover that's too low and not sit flush. Tightening the pan bolt will try to bend the pan and it doesn't bend, it cracks. Inversely, if one side is too high, then tightening the pan bolts will pull down on that side of the cover, off-centering the crank seal which will make it wear unevenly and wear and leak much sooner.
I don't know anything about drilling and tapping the oil pan in the corners. The only oil pan drilling I know of is to drill out the rivets on the factory original gasket or drilling the pan to install a turbo oil return or drilling and tapping the drain boss to repair damage from over-tightening.