This clear acrylic template has the exact hole layout for a pinball pop bumper, including the dimple locations for the spoon switch bracket. The clear acrylic makes it easy to line up. Then tape it down and drill or punch pilots for the bumper bracket and mounting screws. Finally, flip the playfield and make pilots for the spoon switch (careful: these are not always at the same angle). Check the bracket locations before you drill.
This template is exact to pop bumper parts. Many machines, it turns out, are slightly off from this layout but it doesn't matter that much.