One possibility that has come up that you should look at...it happened to a member exactly like you describe...
In the ignitor housing, the points on his had been installed with the long "leaf spring" on the wrong side of it attach point....here is a little screw that this tension spring attaches to and if it is on the outside, away from the distributor shaft, it puts less tension on the points. He moved his to the inside and mounted it and it cured the problem.
Worth a look...you can see the proper placement in this image:
The tenson spring is running from th ponts to the screw mount between the arrow lines for #3 and #4...the screw is directly beneath the #4 line.
Lord send your Holy Ghost into our hearts and make the desire of our hearts Your Will.
Pro-choice, that's a LIE, babies don't choose to die!!