Best to forget using MM58274C, the SGC/GC uses a triple lock to prevent corruption (write to 3 addresses each and every time you need to write to a register). Whereas DS1374C uses I2C link, with bonus of integrated crystal and charger, making it much simpler. Downside, only appears to be available from recognised suppliers (for the price of P/P I could buy several MM58724C off ebay).
Like to knock up prototype and play with I2C bit banging / EPROM paging scheme. Assembler though, none of this C nonsense
![Smile :-)](./images/smilies/icon_e_smile.gif)
Next would be writing Net handler for AVR (assembler). Cheap UNO/Mega with Ethernet+SD shield allows hacking access to W5100 (nothing ambituous in terms of speed, perhaps just tinkering over OPEN#3;'N1_ETH0').
Access to Arduino SD library would be limited to 8.3 filenames (FAT 16/32), so perhaps something like mini QXL file for MDV (similar to Carlos Delhez's *.MDR scheme for ZX)