Very strange, looks like it might be a comparison shot to me for several reasons
I just installed the PAS16 in an LC and I don't see cubic for even a passthru connection between two cards mounted like that. The sound card is larger in width and depth than that L shaped card and a full rectangle to boot.
A custom setup for a stacked board config is the only thing that makes any kind of sense to my coffee deprived noggin, But if that were the case, why not make the bottom card a full rectangle to make room for a the FPU socket? CoPro card is the only thing that comes to mind for use with any other PDS card. It's the only expansion I can think of that wouldn't use the LC's only Slot ID.
Could a 16bit cache card make sense?
Did anyone ever sell an empty socketed FPU card? That makes no sense at all, it should be board mounted unless there's another function.
Looks like the makings of an interesting hack though.