Layed out all drill lines and pilot hole locations for all three ribs. Center and top ribs were fairly straight-forward, but bottom rib with drive horn took some time to understand the plans specifications and become confident in the pilot hole locations due to multiple positions of multiple flanges on the drive horn assembly that need rivetted.
Drilled all #40 pilot holes per the plans.
Positioned ribs and clamped. Began drilling and clecoing center and top ribs into position.