Something I've noticed about Westerly Guild pickguards is that the sizes are all over the map. You'd think there would have been a basic boilerplate size, and hundreds would have been turned out, all exactly the same.
But I have Guilds with pickguards so big that the right side edge had to be trimmed to fit around the bridge, which it otherwise would have overlapped; others that touch the bridge, but aren't trimmed; others that are near the bridge (1/4" to 1/16" or so); and still others that are an inch or more away from the bridge.
TO REPLACE YOUR OLD PICKGUARD: My recommendation is to get a pickguard blank, in either tortoiseshell or black (did Guild ever use any other colors?), and using the one you removed as a sort of template, trace a new one that's approximately 1/16" or so larger all the way around (just enough to cover any imperfections), EXCEPT for that part of the pickguard that goes around the rosette and against the edge of the bottom of the fretboard -- that area should be made to match the old pickguard exactly.
Glenn//.