if you look at the outer ring on the dizzy body you will see a small scribe line, you may have to clean the dizzy to see it, but its where the plastic flash sheid sits there is also a dot mark on this flash sheild at the same point.. (off the top of my head bearing in mind im sat at home with a glass of wine, the scribe is at around the 2-3 o`clock area, if the dizzy is correctly fitted) the rotor arm center will point to this scribe mark.

The phase sensor lobes do not relate to tdc at all.