If it had been done entirely with internal memory resources, the easy way to do this would have been with port I/O rather than memory mapped I/O.

You then could have attached P0 to the data port, P2.(2..0)to the addresses, P2.7 to the START strobe, P2.6 to the OE, P2.5 to the ADC's ALE input, P2.4 to the EOC strobe, and ALE to the clock. Then you'd have to poll the EOC, but I suspect you've nothing else to do while that's pending. It's fewer wires. You then have immediate bitwise control of the strobes, AND it matters not at what rate you operate the 8751, so long as you don't exceed the converter's maximum clock rate with your ALE.

RE