[Jon Stratis]

This is, in my opinion, one of the big drawbacks of pre-machined holes in parts. It's rather time consuming to get everything to lineup properly when you have to make anything custom to interface with it. It's probably the biggest reason my team has moved away from pre-machined holes. Everything we use is simple extrusion, then you just clamp your gusset on it, drill a couple holes through both pieces at the same time, and bolt/pop rivet it in place. Your holes always line up that way, and if you want a nice clean look you just need to properly mark your spacing on the top piece before you drill.