And in the F-body, it's not a structual piece there, just a thin piece of sheet metal. Then bolt down your own seal (I know it's not the magical OEM seal, but it will work).
I knew a guy who had his car for years, needed to swap in a bigger fuel pump. Hadn't decided which way he was going to do it, so he decided to go the cut-way. Pulls off his carpet, and someone had already done it (stock pump must for previous owner must have died). Drove it for years and didn't know, and was sure happy he didn't just pull the tank!