crew cab dually question

[yellowGT]

I dont ever see any questions or info on dually trucks here so I just have to come out and ask hoping someone could help.

I bought a 89 crew cab dually with a homemade solid steel rear bumper weighing about 200 pounds so I took it off and I gonna go with the stock bumper with a hidden hitch behind it. Only problem is that the frame has straight frame rails and not the dipped ones like the suburbans therefore the brackets are different. Does anyone know what brackets go on that bumper? I have posted a dually with the type of bumper im talking about.