After reading the schematics more carefully it turns out that only some anodes are connected to the nMOS drivers, some are not connected, some are permanently pulled up to 240V (the underscore lines).

I'll probably divide the project into phases:

• Phase 1 - connect a replacement of the Logic board
• Phase 2 - find a driver circuit for anodes and cathodes based on modern/available components
• Phase 3 - build an additional board with replacement logic, missing driver circuitry
• Phase 4 - replace the logic board completely

We'll see how it goes tomorrow.