I suggest that you use the serial I/F. I understand that there are problems when using the parallel I/F although I cannot remember where I found this information.

It may be due to the fact that most people have used the serial I/F as it saves on I/O. Also if using a 8051 then it very easily provides the serial data stream/clock using the internal UART.

I will let you have a copy of the IDE HDD schematic/code as soon as I have drawn the schematic. My interface uses a Waferscale (now ST) PSD813F1 with the internal CPLD providing the glue logic, but since the logic is very simple, it's easy to implement using discrete logic chips.