HELP! Slant 6 just doesn't want to go!

Most likely a fuel problem. Try spraying starter fluid down the throat when it starts to die to confirm. For spark, install an in-line spark indicator (cheap at HF). Clip a voltmeter from coil+ to engine ground and see if you lose power when it dies. Before spending a lot of time fooling with points, consider upgrading to HEI ignition or Pertronix Ignitor II.