so, you switched from points to and electronic distributor with larger ford cap and duralast box. Right?
Your 12v should be ran through a resistance wire or ballast resistor before reaching the coil. Should be @6v at coil. Your points system had a ballast resistor (the porcelain thing on the coil) and the electric system uses a resistance wire. If your ballast resistor was good, put it back on, they do the same thing.
If you have the prestolite (75-77), it runs off of 12v.
And my msd runs off of 12v.
Points and duralast are 6v.
Also, make sure your distributor ground (black wire from dist) is grounded. Mine is ran to my dedicated engine ground bolt.
And check for loose connections or messed up wires.
I remember when I did mine. So much reading.