The angle brackets are fairly easy to make. Start with angle iron. I used stock that was 1/8" thick and 1.25" wide (e.g. the flat portion is 1.25"). Then I cut 2" sections of it using the abrasive disk. Careful, the steel will get really hot when you cut it. Use gloves to protect your hands. I recommend clamping the angle iron in a vise to hold it solidly when you are cutting it.

I used the grinding wheel to clean up the edges of each bracket (just like I did for the struts) so that there were no sharp edges.

Then you need to drill them. I drilled mine with a 1/2" cobalt steel bit. Since I use carriage bolts, and because carriage bolts have a square section right under the round head, I use the 1/2" bit so that the square portion fits inside the hole in the bracket.

I put the angle brackets into a vise on my drill press. If you drill them by hand, you should still use a vise to hold them while you drill. You'll probably have the best luck by first drilling a 1/4" hole, and then following it up with a 1/2" drill bit. It is difficult to start with a 1/2" drill bit. Remember to use a slower speed when drilling steel (e.g. ~800 RPM or so).