If that board says ©1991 it will be very interesting to see if you can get it up and running with the PCI Interface Card. I wouldn't worry too much about getting your money back even if it doesn't work out. Someone with a two or four slot NuBus interface Card will likely want to give it a try.
Thanks for the piccie, I missed your question about interest in documentation. Some closeups of the logic would be really good for checking out the missing IC's function.
The chips next to the bus termination are especially interesting, as well as the DIP switch diagram.
A stack of these boxes filled with
Grappler Cards hooked up to a rack full of MoDems in a BBS config makes a world of sense to me. DIO is the only other use I can think of offhand for a multiplexed stack of boxes like this in the six slot IIx/IIfx era.