I'm as sick of these parts as you are about reading them. However today I finished everything short of affixing them to the plane.
First order of business was to pick up a parallel set at Harbor Freight, in order to have a more accurate means of laying out the hole pattern. I searched EBay for these first, and while some more interesting ones came up (notably coated to prevent rust), in the end it was just simpler to pick them up locally.
Using a combination of the parallel pieces of steel, along with some right angles and an ultra-fine sharpie, I was able to lay out accurate lines to drill holes.
Below you can see the final result (there were two brackets in the end), as well as how I accomplished this.
Time: 1.5 hours (not counting the trip to Harbor Freight)