Insert a pin into the hole… if it’s too loose, a drop of CA will keep the little bitc*….umm… the pin in position..
Flip the body over, place the pin in the first string hole. Be sure the body is flat against the table, and drill away…OH.. wait….Congress recessed before allowing any drilling didn’t they?
Drill then move the body, locating the next hole over the pin… repeat until you run out of holes…
You should wind up with something like this..
OK,, so we know where the bridge will be going…. Let’s get those P 90’s situated….
I place the neck and bridge pup in location. Since I’m working off a photo I can only deduce the dimensions by close examination. I’m assuming the neck pup is about 7/16 from the fingerboard, and the same for the bridge pup relative to the bridge. I mark those locations.
I place the middle pup in location and center it using a ruler. The weight on the first pup is just to keep it from scooting every time I touch it.
Ron Kirn