We clamped the tiedown bracket to the bench and screwed on a couple nutplates to pilot drill for the nutplate attach rivets.

We marked which side of these spacers got the countersink for the rivet head, but darn if we didn't get it wrong. Fortunately when I drilled through the spar into these spacers and the tiedown brackets, I drilled quite straight. Even installing the spacers backwards from the position where we drilled the bolt holes, all the bolts fit. One was pretty tight, so we re-ran the bit through to clean it up.

Here're the countersinks for the nutplate attach rivets.

Starting deburring of the rear spar.