I drilled out the holes at work on a drill press.
This was slow. A lot of stacking/creative leaning, to get things to line up properly, and actually sit without falling:
Even still, I'm going to have to pound this bracket a little once its welded to the frame. Both tabs are leaning about 1/32 or so inboard. Not good. But, easy to fix. However, it means that gussets will have to be done on the truck.
Imagine that the firebrick is actually the frame rail, and that you are looking down on the set up from above (ie through the truck, xray vision style). You can see how the bracket mounts, and how the arm comes off of it.