LINKPRL - or Making RSXes Easy, by Harold F. Bower
Banked/Portable Basic IO System (B/P Bios), by Harold F. Bower and Cameron W. Cotrill
High-Density FDC for YASBEC, by Harold F. Bower (Controller schematics, in PDF format).
The ZCPR3 Corner, various Z-System articles by Jay Sage on cpmwelt.de (just scroll down to the bottom of the page).