First, I cut off the oem bumper mounts and cleaned/repainted. This probably wasnt necessary but I like having it cleaned up and it may prevent interference with the bracing on the new bumper.
Next, I made some nut plates from 3/8 steel and spacers from 3/8 aluminum plate. I drilled large holes in the frame so I wouls be able to move things around a bit for alignment. The top aluminum spacer has a countersink hole with a 1/4” bolt to hold the nut plate and spacers inn place.