The distributor is the point of adjustment for the timing of the vehicle. Set just right the car runs fine, off one direction the vehicle runs lean and ric h to the other side. The slots are to allow for rotating the distributor to adjust the timing. Removal is very straight forward. Unplug the wires, take out the three bolts and slide the distributor out. Don't worry the shaft only lines up one way to connect to the camshaft for re-installing. When re-installing the new distributor, put a touch of oil on the oring to allow it slide in easier and limit any damage to it. Set the timing after assembly. You will need a timing light for that.