74LS00 or 74LS08 (NAND or AND). It doesn't matter as they are used just for buffering the output (2 NAND in series, used as NOT doesn't invert the output, so does 2 AND).

As Creative haven't included the optocoupler in its circuits, all the MIDI adaptor cable must have it. You may not see it cause usually they are hidden in the cable terminator.