For some reason I'm thinking they were rear bumper brackets? Maybe way off.
Offhand I do not recognize them. It is very hard to understand your photos without any scale reference in them.
They do not resemble stock bumper brackets.
GT5/GT5-S rear bumper brackets the factory used to install the full L type bumper. They were not impact certified so they could not be used on any real DOT certified conversion. In those days some of the conversion shop could cert a 747 to comply, as far as you new!!!!!
Thanks Kirk. I thought they were bumper brackets just wasn't sure. At some point before I owned the GT5, the rear bumper was removed. That would explain the extra brackets with the other parts.