I was still laughing as I set the router to cut a height of 5.1 mm, but focused in as Peter helped me trim all the way around the face plate. That's still not as thin as the plate will be when all is said and done, by the way--as always, a few extra millimeters are left spare, to allow for goof-ups. As anyone who's worked with wood (or cooked a meal, for that matter) knows, it's much easier to take off a little bit at a time and get to a point slowly, than to go too far and be forced to redo the whole thing. You can't add wood back!
It's rather hard to see in the following photo, I know, but resting on top of the faceplate is an "arching guide," a simple model made from original blueprints of the original Guarneri, showing the desired arc of the top from neck to tail. When the guide rests against the plate, it's easy to see how much the curve needs to be adjusted--i.e., how much wood needs to be carved away from the contact points--so that there are no gaps in between them.
For the aforementioned carving, I got to use another of my favorite tools--the finger plane!
[I realize how girly the thing I'm about to say is, but I can't help it] Isn't it adorable?
By the end of the day, I'd produced a reasonable facsimile of the correct arch. However, the plate's still about 4 millimeters thicker than it needs to be--so when I come back in later this week I'll continue whittling it down, preserving the curve as I go.