Any chip will do, but dual bank chipc are the best for you. One for a normal BIOS and one for this special unauthorized one. You first boot the unauthorized BIOS, reprogram the eeprom, then change to the other bank and boot from the normal BIOS. Install the HDD, LOCK it (save the key and other stuff), then you can remove the chip if you need, and the machine will work fine with original games. (of course you have to reinstall the original dashboard aswell)

regards, Stephen

pS: cheapest chips that offer dual banks are Duo2X and Xchanger2.