I started making the hold-down brackets. I decided to use 1/2" x 1/2" angle, which I riveted to the underside of the aft track. The holes on the top side needed to be large enough for my custom ground 1/4" 100 degree countersinking drill, then I deburred them with a chamfer and filled the holes with JB Weld (the chamfer will stop hand pressure from pushing the plugs down and out). Later, it won't even be apparent that there were holes in this part.