We didn't use one, and maybe that wasn't smart, but my engine is extremely difficult to find timing references. We rotated the motor by hand so the rotor pointed at the #1 cylinder on the distributor just after the compression stroke. You can kind of feel the motor is hard to turn, compression, and then the rotor "jumps" quickly once the piston starts back down. Back up slightly and you should have it. This was about the 6 o'clock position in the distributor. See the video. My goal was to put the new distributor in EXACTLY the way the old one came out. I very carefully extracted the old distributor. Be aware the rotor "unwinds" CCW about 120 degrees when you pull the distributor up. I very carefully inserted the new distributor the same way, and it seated right at 6 o'clock. This is not well covered in the video. Looking back we should have shot a timing light on the marks before, and now would have been the time to make sure the timing was where is was before starting. It probably needs to be reset, so the next sunny day, I may spend finding my marks and see how close they are to where they should be. I am not a mechanic and don't recommend doing what we did. I did have a mechanic friend help, so I am a little assured we did a little something right! Ed makes it look so easy on the video! I am anxious to hear from knowledgeable mechanics on this subject... Sent from my iPad using Tapatalk