"The rotor is past the terminal boss for #1 when the LED lights up" The LED light should be setup before reaching #1, not after.
"There is no #1 mark on the rim, like every Bosch I’ve ever touched." you can pick any one of the six points as #1 if the firing order and TDC is properly sequenced to that point.
If your CDI has a built in advance(like my Classic retrofit CDI+) you have to use a timing strobe to calibrate TDC with the coresponding curve in the phone app.
Also, my car with 123Ignition the idle was unsteady when I had solid copper core ignition wires.
https://youtu.be/-9SgWGRqoLM
After sorting out the bugs, my car runs smoother from idle to redline with 123Ignition compared to the original rebuilt distributor with Pertronix.