Thanks for your description. Yes, the 555s were already handled by faking a variable resistor at pin 6 (THR) instead of pin 5 (CV). The result is the same: the output pulse time varies between two values.
The /SRST section with the 3 transistors is what needs to be black boxed. You are right: R20 (220) was tied to the wrong end. It connects to the collector of Q3.