John Martin said something like:

....[snip]...

I've got one trick of my own. As I do a lot of metalwork, I've made
up some transfer or spotting screws. These are somewhat like dowel
spotters. A large flat head just as thick as the distance between the
hinge leaves when closed, a short shank of the diameter of the hinge
hole, and a short point sticking up past the surface of the hinge.
Soft steel is fine. Mortise and screw the hinges onto the box bottom,
then open the hinges and place the spotters through the holes. Close
the hinges down on the spotters, and you'll now have points sticking
up where the screws need to be, so position the box top and tap it
lightly to mark the screw holes.

John, could you post a link to a picture of that thing? It's obviously
nothing I can make, but I am curious.