Making sure that the number one piston is at TDC compression install the intermediate shaft so that the slot is parallel with the engine center line. Install the distributor and note where the rotor is pointing. Install the number one plug wire in the cap terminal where the rotor is pointing and follow the firing order around counter clockwise. This is for uniformity sake. In the real world it makes no difference where you install the slot or the distributor as long as you have the number one piston at TDC firing and install the number one plug wire in the cap in the corresponding cap terminal and follow the firing order around.