Yes the tr3a bumper is a difficult fit. The tr3 is easier to fit because the brackets hang under the apron and do not go through the apron.
The way to fit the tr3a is to let the brackets hang untighten at the beginning then go around and tighten in place after all the pieces are in place. The 2 inner brackets need to line up with the holes in the apron and need to slide kinda, so that the bolts can get started and not damage the apron, but they need wiggle room.
Do not try and tighten or snug up the inner brackets early because they will push and pull everything around too much.
The 2 inner brackets came with a threaded nut to accept the bolt that comes through the front of the apron. If you can get the inner brackets close to fitting at the holes in the apron, then the everything should work. If not, the apron might be too far out of line and need to filed and slotted some. The inner brackets are difficult to bend, but you can gain some room there also.
I worked at trying to get all 4 points of fitting perfect and found it very challenging, so I settled with getting close and tightening as a whole unit.
steve