Slotting the mounting plate on the sensor gave a "hard" unadjustable 2 degree advance on the ignition. With the low compression engine I have never noticed any knock when the engine is hot. It's proven better than nothing but.....
  Got the idea from when I built go-kart engines using the Briggs 5hp. A common trick was to use offset flywheel keys to kick up the timing, some builders also slotted the mounting holes for the ignition coils.
  Setting up an adjustable advance is a whole other ball game, the ignition isn't like the point type where it was possible to respring the weights and change the advance curve. Now it is all electronic controlled which is why a schematic of the ignition module would be so helpful. Even then you would still need to figure out which components to change to get a custom advance.
 I've found that low compression engines like the big single don't do well with a lot of spark advance over the factory settings, a little goes a long way.  Change the advance curve should help in the midrange torque while the "hard" advance on my engine seems to help overall.
 Just for sh!ts and giggles I'll see if I can track down a schematic of the ignition module, it would be a nice piece of reference material to have on the site. Officially retired and have plenty of time on my hands.