Thankfully I haven’t taken it off or even disturbed it but due to it not running smoothly and finding a couple of previous 'Cowboy' fixes, I thought I would get all the needed data together before going further. That manual seems to have all the air gap tolerances except for the model I have.
The section stating
either marking the unit before removal or using a makers location tool to refit correctly
refers to the 2 & 3.5hp engines
After re-reading page 4-45, and even though it does not actually state it, I have come to the conclusion that on this model it is not adjustable, which seems a little bonkers.