....pin 22 (nOE) is wired to IC73 pin 25 (nRDS) and pin 27 (nWE) is wired to IC73 pin 24 (nWDS)
Hmmm..... If you read any of the installation instructions in the thread, you’ll see that I specified RnW and WnR and that in response to another user having issues with nRDS and nWDS, I tried using the latter and found that they don’t work reliably for E2, if at all! Can you try using RnW/WnR please and see what you get - I originally suggested IC14 Pin 1 and IC33 Pin 11 for a Model B but they are available at various places.
In the end, the Master config I specified was cartridge-based only so I voided the Master references in the above schematic.