Welcome to the forum 82swb. I am trying to get a visual of what your concerns are. I "think" what you are questioning is the bolt on notch would not leave a clean mounting surface directly behind the axle where you want to mount the upper bag brackets.
If this is correct, you will need to find a practical solution. When we did my system, a bolt in notch was never considered since the shop builds all their C-notches in house. The weld in design left the frame clean in the area needed to install the upper bracket.
In your case, it will require that you consider having your bolt in welded in after its installed, or make mods to how the upper bracket mounts. You might be able to drill the bag bracket to clear the bolt head, or run spacers to move it away from them.
Oh yeah, INSIDIOUS '86 lets see your air suspension? "Sorry couldn't resist"....
