Ok, one last posting to this thread - I mentioned in a previous post that the pin numbering on the switch didn't seem to match the schematic. Now I know why.
I own two of these controllers, both Series 5. Per their date codes, they were manufactured five weeks apart in 1969.
Before today, I had only looked inside one of them. Today I opened the other. Lo and behold, the switch in that one matches exactly with the schematic. It looks like someone replaced the switch in the first one at some point with one that's similar, but different, so the positions on the switch are mostly different than the normal one. No wonder I was scratching my head looking at that switch diagram !
Thanks for a great discussion ! I just ordered a cheap board with four 5-volt relays - it was cheaper than buying the relays separately, and I already have an Arduino Nano lying around which will drive the relays and give me a USB serial port on the PC. Should be fun to add some smarts to this 50+ year old controller.