There a couple of options on the rear bumper: with the rubber stripe or not. Also, if you have bumper guards or not (which also has the rubber stripe, or not).
This car has the rubber strips on bumper and on bumper guards.
This car has neither rubber strips nor bumper guards.
Inside of the bumper is a heavy bumper reinforcement. Freight will be a lot less if you didn’t need the bumper reinforcement (it weighs more than the chrome bumper does). There are also two bumper shocks that attach the bumper to frame.
I’m assuming the “plastic bumper thingy” you are referring to is this:
If so, that is the bumper filler. There are three rear bumper fillers: top and two sides.
As far as I can recall, the bumper fillers fit ’78-79 F-body only (and maybe ’77-79 M-body).
Note: I do not have any of the items you are asking for.
Note: You might take the chrome bumper to a bumper shop. sometimes they can rebuild one, sometimes not.
BudW