Question regarding 74HC574 (question very difficult to word)
My, it's been a long time since I worked on Z80 stuff. Perhaps you could use one of the address lines to trigger the latch pin and use one address to set the data then the other to set the latch? You really should check the timing datasheet to see if you even need it though. It looks like you get about 1/2 a clock between the data lines being set and IORQ or WR being set.



Edit: Oh, I see what you mean about not keeping the data pins constant.