I did it while the back was still off the engine.  I had decided that I wanted the sensor to be located on the bottom of the engine.  I then placed the crank at TDC and rotated the crank 28 degrees using a degree wheel.  I then marked my hub for the magnet where it matched up to where I wanted to mount the sensor.  The engine is mounted inverted on my airplane so it is real easy to see the sensor and make adjustments.  To get to the sweet spot, I moved the sensor a couple of degrees counterclockwise as seen from the front of the engine. 


Jim