My nephew stopped by today and helped me install the rear bumper assembly on the truck. The brackets fit nicely on the outside of the frame rails (just a little minor prying with a large screwdriver). Once it was slid on, the buttons on the rivets popped into the holes in the frame and held it there while I installed the bolts. Bumper and brackets fit well and look good.
The CounterPart splash apron, not so good. It already had the issue with two of the five mounting tabs not being located correctly, that I had to fix yesterday. Today I discover it is not bent correctly to sit flat on it's own, so the edge of the apron (away from the bumper) angles down, more on one side than the other. It needs some of spacer between it and the brackets, near the truck frame, to hold it up and level with the truck bed. The bigger issue is the curved pieces on the sides, that are supposed to fill the space between the bumper and the back of the fender are about an inch too short. There is a full inch gap behind each fender. I am going to take it off and fabricate something, which I should have done in the first place.
Thanks again to everyone who replied.
Rear apron was not O.E.
Fabricating something good idea
For my front and rear brackets I used extra long bolts held loosely to start all the holes, then drew everything up. Once made up swapped out the long bolts one for one.
Still needed to use a ratchet strap on front brackets.