I have for 10 or more years used CPLDs from atmel and xilinix. you can program the chip to do exactly what you want and with memory-mapped-I/O you even include the address latch and thus get all you need in ONE chip external to the '51. One major advantage of this approach is that if you made a mistake, you reprogram the chip instead of redesigning your PCB. Once, in order to interface to a unit with no information, I actually made a logic analyzer which after completed analysis was reprogrammed to be a driver for the bus. Two radically different functions without cutting a trace.
Have fun
Erik Malund