Outer bumper brackets

Can someone enlighten me on outer bumper brackets/insulators?
My 65 Bcuda has rubber insulators between the bumper ends and rear quarter that should fasten to the quarter panel. There’s no mounting holes in the bumper at this location.
I bought another rear bumper in a parts lot that looks identical with the exception being small S shaped brackets that fasten to the bumper ends w carriage bolts, and threaded to accept small bolts from inside the rear quarter.
Im curious- Is there a difference between Valiant/Bcuda? A difference between 64/65?