Most people in the shop at the time used the octane selector to set the timing, because that bolt is easier to get at than is the 'proper' screw behind the distributor, and the octane selector wasn't used for its original purpose- which Tiny explained. In the picture in your manual, the square nut behind the distributor is the other end of the 'proper' screw, which is often difficult to get at. If the timing is off very much, you have to loosen the clamp and turn the distributor to get the timing where you need it- ball at the pointer, with the octane selector at zero, as originally intended.
Also, if you are wondering about the big cup behind the vacuum advance chamber, its a grease cup. Clean it and fill it with fresh chassis grease and turn it in a little every couple of thousand miles or so. The original specification was every 1000 miles. When the cavity inside the housing is properly filled, the cup resists turning- if it turns freely, like a loose nut, keep turning until it resists. The grease keeps the bushings lubricated.
Harvester
