Rust Bucket, this may be a dumb question, but how do you know the misfire is affecting all cylinders? Have you checked the plugs or done a compression test and found all cylindeers to be identical?
Have you done a tune up, including a valve adjustment, even though the "mechanic" says misadjusted valves rarely cause the poblem you're having. It seems that in order to isolate the problem, first all of the variables (timing, valve adjustment, carb adjustments, etc) should be checked along with tightness of intake manifold and carb mounting bolts.
I have had two Crane Cams electronic ignitions fail in my '71 Dodge van that I bought new. In both cases the ignition failure caused intermittent misfiring that varied from very mild to actually shutting the engine down. Do you still have the points to try? If not, a D105 point set will work, because it fits Delco distributors from the 1920s through 1962 even though it's not listed in parts books for the old vehicles. I have that point set in my 1936 Chevy engine.
Good luck!
