I also tried to make a gameboy eprom cartrige. I used this schematic (lower left corner of the page):
It did not quite work, I have no idea what went wrong. When I burned an eprom and turned it on, most of the nintendo symbol came up, but there were a few missing pixels and it did not work. I know the eprom was good and the burn was sucessfull.
If you do find a plcc eprom/eeprom/flash chip that is 32k and 44 pins, you can not just replace the masked rom. it is a different pinout, you have to get the cart connector pinout and wire the chip according to it.