Today I drilled all the holes for attaching the spacer blocks. I started by clamping an ddrilling to the 745 rib after removing the mddle subpanel for clearance (pic 1). Then I created a plate to recreate the skin and hold the key ribs and bulkheads in alignment. If I placed the skin, it would have been a more difficult reach, so I just backdrilled through the skin holes onto this plate (pic 2), then clecoed in place while I drilled. In pic 3, the final result held in place by temp bolts.