Got it. When I machined mine I bought 1-1/2" thick stock. This gave me 3/8" of an inch, or thereabouts, to hold it in my vise. Setup 1 was to machine all of the top side details and the perimeter. Setup 2 was machine the bottom side to achieve 1-1/8" thickness. Setup 3 was as you described: clamp part to angle plate and drill/tap the parallel mounting holes. You could certainly do it as you have laid out. I see no down side to doing it either way.