SamQ aka Ah! Q!
Old Oak
Sam, getting back on topic, you suggested a router. Not sure if you realise, but all of the drilling is in a vertical orientation (the bookcases are already installed).
Adrian, I'm not sure if you realise, but I didn't. Mention using a router. I said...base like wot is used on some routers. I refer the right Hon Gent to Bill Hylton's entertaining treatise: "Router Magic", pp50 et seq, where the Murrican Guru goes into good, methodical detail. Yes, William is a router afficionado....BUT...the principle applies, especially for engraved cross hairs method (of lining up a drill bush instead of a router).
Yes, I did know also you were facing a difficult task - with potential embarassment if you failed - on a narrow access, vertical bookcase component.