We wanted to run about 15 degrees of initial advance (at idle), and have the engine timed for 35 degrees total (at full mechanical advance). That means the distributor needs to provide 20 degrees of mechanical advance instead of the 30 in the factory plate. To shorten the mechanical advance, the slots need to be shortened. The slots in our plate measured .480 inch long. We zapped the ends of the slots with a MIG welder to get some of the advance out of our plate.