I have also developed and produced a simple backplane PCB allowing up to 5 PCBs to share the Data and Address lines of the HobbyPCB 65C02 SBC. It has the same pinout as the SBC, and Floppy IF board so allows easy connection to each other. There is a 2k x 8 (32 rows by 64 columns) now available, and an extension RAM PCB (coming soon) which uses the same pin layout as the other boards so connecting is made very easy.
The backplane PCB has provision for a reset push-button, as the SBC's reset might be obscured by an additional board, an on/off switch. Space for an RS232 Dongle, and a 5V PSU connector.
This PCB allows the expansion of the 65C02 with a variety of add-on PCBs. They can be plugged in in any slot, there is no set position as each board picks up the Address, Data and Control Bus as needed.