Thanks. And code found and implemented.
It uses an interesting method of HALT and Interrupt to trigger its timed actions, and luckily the code is simple and repetitive so it was easy to understand.
I'm thinking to use the R6.5 interrupt to signal that serial input will be incoming, and then either initiate the selected timed sequence or set up a different timed sequence than the front panel indicates.
There's an I/O on an ESP01S which I can use to trigger the interrupt on R6.5, and handle the added functions.
Otherwise the rest of the code should be unchanged so the front panel works as expected.
Since the EPROM is UV and there's no option for 2732 in EEPROM, I've bought some AT28C64 devices that I can use with a simple spacer socket to do development on.
For production, I'll put the final build back on the original 2732s, as there should be enough space.
Any thoughts on the plan?