Step bumpers; I REALLY need to know!!!

[El Jay]

This may be a tad long, but I think everybody that may be able help needs all the details.

I'm the 3rd owner of my '72. When the original owner took delivery from the dealer, it had an 11', slide in, cab over camper that sat clear back on the tail gate. So the Step bumper sat back beyond that.
The friend that I bought the truck from dumped the camper. He had a "friend" remove the extended step bumper. While doing so, said friend also cut off some of the right frame rail with a torch. But there is still a ton of the old step bumper brackets still welded to both frame rails.

This past weekend, I helped my cousin take off the old step bumper that was on his wife's pick up to install a "sport" bumper.
We ran into some welds on her truck that had to be ground out to get the old bumper brackets off the frame rails.

After all this; my question is, is there any legal requirement that a step bumper has to be welded to the frame, rather than just bolted?

The reason I'm asking is that after I get all the old junk off my frame rails, I'm going to install my cousin's wife's bumper on my '72.

I really don't want to weld it after it's been bolted on.
I'd rather that it be able to "float" a bit if some MOE-RON decided to rear end me; so the bumper moves but the frame rails don't.

Thanks to everybody in advance that can help me on this.

Neither my truck, or hers, had receivers. Just balls on the bumper.

El Jay