I have the repair manual for the 4951C which was the early model of the 4952A. The unit is effectively the same but the main board and memory board are totally different.

The one thing that is exactly the same is the floppy controller board. From this schematic I have verified that all the "double wave" logo'ed ic's are in fact National Semi GAL's. This means the bus decoding is inside the black box and requires probing to identify. That is no simple task.

The floppy board did give me the complete riser pinout though, so from that I at least know the interface. If I can isolate things to similar components I may be able to find a starting point.