Ну вроде у него же написан тип микросхемы
(best) decode the IN #FF port and make a real read from the video data bus, by means of three-state buffers - like 74LS125 or 74HCT125 - between the D7 of the video RAM and D7 of the auxiliary (full-speed) RAM

74LS125 = К555ЛП8
74HCT125 = КР5564ЛП8