Finally determined Nutplates for the Flap Weldment attachment were the wrong size, so finally I drilled out the nutplates and AGAIN, they were the wrong size, installed at the Van's Factory. I replaced these with the correct size as best I could. Not the pretiest riveting job by any stretch of the imagination, but it is strong. Once this was done, I was finally able to temporarily bolt each bearing block in place and match-drill the forward hold into the Ouboard Seat Rib Angles.
