Ron's timing notes are fine but I would suggest the following. If you are happy that your timing is correct. Check it with a strobe at about 1500 revs and note/mark the timing position. Fit the Pertronix and repeat the timing again with the strobe. Not unusual for the Pertronix to skew the timing one way or the other a little due to magnet positioning. If wrong, readjust the distributor to return it to the original setting. Job done. It's very unlikely that just fitting the Pertronix will bring about a no start situation after fitting unless something else has been disturbed or wrongly connected. Even with quite a big timing error, the engine should still start. Having the engine warmed up before the changeover makes for an easier start.