Bidirectionnal Interface Between 3V and 5V Buses

I am presently designing a few computer boards, for experiences, and need a simple way to interface a 5 volt data bus (indeed in NMOS, so nearer the LS-TTL than CMOS) to 3 volts level (for NAND EEPROM and 3V mixed devices).
Although the bus is specified at 20MHz, I shall at first work at 4MHz, so that slow devices are sufficient.

I have no previous experience with new fast logics such as LV TTL and so on.