Yesterday, I drilled the right-most forward fuselage ribs to the sub panel (no photos, sorry). A post-drilling check seemed to indicate that I had drilled it slightly (~1/32") to the right of the desired position. I was frustrated and called it a day, but after some checking today, found that the gooseneck arm was slightly tilted...presumably due to welding stress. I clamped it in a vise and twisted it straight. That cured the offset.

Before drilling the right inboard rib, I set the spacing, but found that using a 3/4" block would have been too tight, because the gooseneck arm was about .008 thicker than the nominal material thickness.

I dug out a .010 shim to space it out slightly before drilling.