I started by closing up the F-785B attach angle to the prescribed 87.5 degrees. I should have done this BEFORE cutting the corners off of the vertical leg. As it was, I had no bending leverage where the corners were gone, and it took a lot of fiddling to get that leg to some semblance of straight.
I then drilled the F-766C plate to the channel, then prepped and primed the plate.
Next, I fit and drilled the F-758 brackets to the bottom of the F-766A channel, then prepped and primed the brackets. I then reamed all of the rivet and screw holes in the F-766A channel to final size, then riveted the 8 nutplates and 2 brackets to the channel (photo). Note to future self: If you ever build another RV-7, follow the instructions and rivet the brackets BEFORE installing the nutplates...