I fixed bugs from the initial version (inverted PS/2 connector, fixed SD card part layout, rearranged the connectors) and now RetroWiz mainboard "alpha" version is assembled and tested. Please download the Eagle files below.
Several hand-assembled boards are also available on Ebay, see Store
Download eagle files: eagle.zip
How to program the mainboard
Use any AVR ISP programmer to download the program through ISP connector (MISO, MOSI, SCK, RESET, GND). I prefer an old AVRISP MKII from Atmel or ZeptoProg. All of them will work.