I deburred the z-brackets drilled one center hole and drilled them to the to main spar. The procedure was as I did for the left wing, i.e. I deviated from the plan and followed the method many other builders choose in order to get more space for the pull rivet (when riveting to the fuel tank baffle).
After getting all holes drilled, I drilled the nut plates to the z-brackets and countersunk for the nutplate rivets.