A whole slew of these notches are needed in one flange of the F-703B angle. I'm way too lazy to do all of these by hand, so...

I decided to make a jig and use the router to do the hard work. I'll use a 3/8" diameter guide bushing, so I drilled the root of the guide notch with a 3/8" brad point drill.

Glued on a clamping fence to the underside of the template. This clamping guide is tipped backward by 2 degrees to make it easier to achieve the correct depth notch without causing a gouge in the other flange. Used a couple brads to hold it in place while the glue dried. My router guide bushings and 1/8" diameter router bit should arrive tomorrow.