I completed fabrication of F-766C plate by match drilling the rivet holes to the F-766A channel, then countersinking them. I then prepped and primed the plate, riveted it in place, and final drilled the bolt hole.
I fit and drilled the F-785B attach angle to F-785A channel. After taking photo 2, I noticed I had mis-positioned the angle by placing the bottom of it 1/8" higher than the bottom of the bracket instead of 1/8" lower. I have ordered a new channel, but will re-drill the angle in the correct location on this one and continue work on the flap system.