I started by closing up the angle on the F-766B angle to the prescribed 87.5 degrees. I should have done this BEFORE cutting the corners off the vertical leg. It took quite a bit of fiddling to get that leg back to some semblance of straight.
I then drilled the F-766C plate to the F-766A channel, then prepped and primed the plate.
Next I fit theF-758 brackets to the bottom end of the F-766A channel, then prepped and primed the brackets (aft side only). I then drilled all of the rivet and screw holes on the nutplate attachemtn points to final size and deburred the channel. I then riveted the nutplates and brackets to the channel. Note to future self: If you ever build another RV-7, follow the directions and rivet the brackets BEFORE the nutplates...