Changes

The main component on the PCB is the EPROM itself. This may be any pin compatible 8x128k (8 virtual ROMs) or 8x256k (16 virtual ROMs) part such as the 27C1001 (8x128k UV EPROM), 27C2001 (8x256k UV EPROM), 28F020 (8x 256k Flash EPROM). The EPROM should have a response time of 200ns or less. The five other ICs are standard TTL Logic devices and only need to be of the type 74LSxx (74HCTxx, 74Fxx etc will also work but are not necessary in this application). The unconnected pins on the EPROM in the schematic above, should be connected to the associated Address and Data bus pins of the 50way connector. I just left them out for clarity.