From what I've understood, you want to build a 'magic' board that looks like a graphic lcd display to an existing system and the generate video as would be displayed on the graphic lcd. Sounds like a job for a fpga methinks - it has to emulate the toshiba t69xx graphic controller, store the bits into some ram and some hardware to read these bits and display on a monitor. Its 'doable' but I think you'll need digital logic design skills rather than electronic contruction skills.