I received the PCBs for the cartridge and the programmer.  I've built them up, but haven't started programming.  I'm still working on the Arduino code to load the software.  I used two 8-bit shift registers to hold the address, and then I directly interface the data bus for each chip.  I can control the output and write enables independently for each chip, so I can combine the two data buses.  This lets me read and write the whole address space for each chip.  I have to admit the cartridges are pretty sweet and a nice size.  Maybe I'll put together a 3D printed case for it.  Unfortunately I didn't think of putting in any mounting holes for that.