I have a pan almost identical to this one somewhere.It was off a impala with a crate engine bottom welded on it.Home made for the mud bogger which is what many guys were running that ran BBC at the time in that sport. BBC Vette pans as far as I remember are the same from 65-74 and like Chuck says not two stepped and don't look anything like this l88 or not.
I would say it looks like a homemade pan ended up in the GM box at one time.Cannot grasp anyone not seeing it was not original and paying 1000.00.
I better find mine and get it on e-bay quick.
But I don't have the box.