Recently found Z80 video of how a guy makes ZX Spectrum computer from ground up, fixes bugs and problems as he proceeds. Video is in Russian, but still amazing even if you don't understand it!
Actually there is now design out of 74ls series logic that replicates functionality of the ULA (it is probably completely bug-for-bug compatible), IIRC it was designed by author of said book.
Nice, I'm thinking about making it possible to connect it directly to a display/TV and keyboard. Now, I have to have a terminal or laptop + terminal emulator.
https://www.youtube.com/watch?v=8rWCYo1UcOQ