Although not assembly line correct, they seem to bring pretty good money. Have seen them for $600 and up just the bare pan and a lot more when packaged with the studs and corresponding windage tray.
https://www.ebay.com/itm/14522233099...3ABFBMrpid2tVi
That pan was still available over the counter from GM until almost 2010. Less than $100 bucks at the time.
As for the differences between assembly line and NOS, I wrote this comparison piece 13 years ago:
https://www.camaros.net/threads/nos-...l-pans.178450/