The doubler plates need to be clamped securely in the correct position on the rear spar and then match drilled.
I used my cordless drill and the drill reflection to maintain perpendicular holes.
Pushrod Holes
Two of the doublers cover the aileron pushrod holes in the rear spar, so these need to be cut out in the doublers.
Hole position marked.
I used a step drill to remove the bulk of the material, and finished off by filing.
Then I clecoed the doublers back into position on the spar and gently filed the doubler hole to match the spar hole exactly.