Some of the holes in the rear spar are final drilled #30, where they coincide with the ribs, W-00007B & W-1007C doubler plates. Also where the W-1013 Inner Aileron Brackets attach. First of all I set to and deburred all the parts … groan!
Here is an inner aileron brackets clecoed ready for final drilling to the spar. The picture below shows the additional doubler in front of the spar as incorporated by the Service Bulletin SB16-03-28
As you can see, rather than final drilling, I final reamed! I clecoed alternate holes for the final reaming. It’s easy to lose track of which holes have been done as you swap clecoes, so I found it best to mark each hole as completed.