Tony - Memphis
A couple of thoughts...to mark your hole spots, I have seen a tip where a bolt that fits in your mounting holes has its head cut off and is filed to a point in the drill press (or a drill). You make however many you need for your base and when you get the router in place, a good rap on the top or even just hand pressure will mark the spots to drill your holes. To center the router in the opening, there is a centering bit out there and you can make your own on the lathe. One technique uses a collar in the table (assuming yours accepts them) and the centering bit is the same od as the collar id. Some have a taper as well. Finding the metric bolts can be tough. Lowes and HD have some in their unique item bins. I have had to oder some too. Good luck.

Tony