Please take this as only my opinion, others may disagree. I'm not trying to discredit your attempt to make things perfect, but it seems like you are putting a LOT of effort into making the holes perfectly, where in return there is no way that you will be able to drill them to the precision of your measurements. The last thing I want to do is insult your abilities and concern, but you will never drill the hole perfectly, even with the proper tools. I am all about getting things made as close as possible, but I make myself draw the line somewhere before I kill over worrying about something that I will never notice the difference between "better than good enough" and perfection. Yes, in this case close alignment is the only way to go, and guessing the center just isn't good enough, but I think your taking it to the next level. Again, I'm not trying to be a turd, only trying to help and maybe ease your mind on the matter. Anyone disagree?