The brackets are currently a non-factor... the bumper won't physically go on far enough to even try getting the bolts in the brackets.
The pins either need to be cut off, or I need to enlarge the holes they go into. Considering I don't think they help at all since the bumper sits on the rear "shelf" of the unibody, i'm thinking grinding them off is the best option.
Though I like how Mark put it; gonna head to bed soon and start with a fresh mind tomorrow