On one of my 4ac's there was 2 markings on the gear (4ac & 2ac) with a hole under them, You have to join the 4ac hole with the notch behind the gear, Its not that hard to see.
EDIT: I just checked the 4AC out of the AE71 and its only got one marking so i got some pics for you:
I dont know what the actual timing degree is on the 4AC so i just labelled it - & + 10
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