Added more wire ties to prevent vibration of wires and to keep things neat (photo 2).
Photo 1 shows my center panel removed, and the wires coming from the ZTron switch/breaker unit. I have to say, I had high hopes for this thing, but it doesn't work out of the box, and does not come with a computer interface that works with a modern computer, so you have to buy an adapter before you can even program it. And the customer service is adversarial and condescending. They said that not having a 9-pin serial port in my computer (actually, I tried 4 different laptops and a desktop and NONE of them have such a port) was a "defect" and was my problem, not theirs. I CANNOT recommend this unit or the company at this time.
In photo 3 I simply put the cylinder numbers on the intake manifold with a sharpie. I have the painter's tape temporarily on the cylinders in the photo, but of course those won't stay.
View behind my center panel, with wires from the ZTron switch/breaker unit.