This turned up in cleaning up the shop.
There's a base bar with three attachments. First a round bolt of adjustable angle, the pivot has angle markings "88, 68, 59, 49, CSK". The other two form an axis and have an angled bed as if for something round. One attachment screws down to clamp what's held. The other pushes a base plate along the bed axis. There's also a little plate on the front, able to stick up into the bed's path but without quick adjustment by hand screw.
I'm thinking it's more likely to hold a tool than a workpiece, perhaps knives for turning? What are those funny angle numbers?
There's this other item, a disc cutter for short pieces. It shows the same colors though I don't see where the first thing would be mounted, so it might be a red herring.