Do you have to plug of the vaccumm line coming from the distrubitor to set the timing?

Yes, you typically need to plug the vacuum line coming from the distributor when setting the ignition timing. This is important because the vacuum advance can affect the timing reading; without plugging it, the timing may appear advanced due to the additional vacuum signal. Once the timing is set correctly, you can then reconnect the vacuum line. Always consult your vehicle's service manual for specific instructions.