If it starts intermittantly not sparking on every cylinder, the coil is usually shot. from what you are describing though, I'm suspecting that you have a problem between the negative coil terminal and the plate where the points ground. Things to look for:
1) points that are burnt, pitted and bumpy indicating that they have stuck
2) check that dist shaft has no horizontal play, causing varying dwell
3)point and condensor wires that are internally broken and/or grounding... look carefully at all wire ends,even where they come out of the condenser... look for (arcing) burn marks. This goes for the wire that goes from the dist to the coil, as well. Where the electricity goes thru the side of the dist housing is vulnerable to grounding
4)Like somebody else said, change the condensers
5) I've seen ballast resistors that are intermittantly bad when they get hot. Eventually you'll know this problem by the fact that the engine will start but immediately stall when you release the starter switch. This symtom indicates that the full-time hot supply to the coil is broken and that the full-voltage bypass wire from the starter solenoid is solely supplying hots while cranking.

Your description of sudden intermittance doesn't sound like a fuel problem, but if you've got a transitional stall during acceleration, there are a couple of transitional fuel circuits in the design of all carburetors. Choke operation and pump shot can be easily checked visually.
If you know and have checked all these things great! I hope I've been helpful and not taken as condecending by discussing basic troubleshooting tactics. If you guys are way beyond me, I'll shut up and go to my room ;>