When it dies try opening and closing the points by hand while checking for spark at the coil wire. If there is no spark and the points are ok it is most likely the coil. A better test would be to disconnect the distributor at the negative side of the coil and using a jumper wire short the negative coil post to ground while checking for spark at the coil wire.
Also a good first test is when it is not running check to be sure there is voltage at the positive side of the coil with the key on.
I have a wiki article on troubleshooting ignition that will bring you through it step by step. Just search the wiki for ignition troubleshooting.
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