Don't know if this will help but it sounds like your troubles started after the electronic ignition was installed, when I put the Pertronix on my V8 460 I had the same problem, miss firing and very difficult starting, did some research and I was sure it was wired properly, one of the posts said to add a 1/8" thick rubber washer (I made on by cutting a piece of hose) on the distributor shaft under the magnet, I also had to shave the same amount from the bottom of my rotor to make it fit, worked perfectly after that fix, I guess it had everything to do with the position of the magnet inside the distributor.