Barry and Dave,
You can't really see the markings on the motorhome in the usual place, and that is why they put markings on the underside of the coach. The indicators are 180 degrees from the topside ones, so you have to set up on #5, which, I believe, is 180 degrees from #1. Or so I have read here.
I have not taken out the distributor, but perhaps a PO did so. I have had this coach a long while, and it always wants high test or it pings. I am envious of those of you who are able to use regular, so I am trying to get to that point if I can.