Oh Doctor, Doctor...

I have a vintage pre-war Martin dreadnought and have long wanted to add a second neck to it so I don't have to switch guitars when I need a 12 string. I recently found an old broken 12 string neck in a yard sale and bought it for the bargain price of $450. Can I just glue this to the upper bout of my Martin and string it up?

Actually, the question is kind of moot since I already glued it there (and used a couple of wood screws for good measure). The real question is: "How do I figure out where to drill the holes in the existing bridge for the new 12 strings?

Don't worry... I have a very extensive workshop's worth of woodworking tools, including a ballpeen hammer, a Sears Craftsman 3/8" drill (with only one bit, a 11/16, but how many do you need, seriously) and a Barlow knife with a broken blade.

(p.s. hurry with your response please... I have an important gig tonight)