I had a 350 engine that had an intermittent miss.
I started changing out the plugs first then the plug wires and yet the miss was still there every once in a while.
I then changed the vacuum lines thinking maybe the spark was jumping around but that was not it either.
I then pulled the distributor thinking the shaft might be shorting out from time to time but that also did not fix the problem.
We checked the battery and all kinds of stuff with no luck.
A good friend of mine who is in his late 70's told me to try one quart of Marvel Mystery Oil and when I asked him why he said I think you have a lifter that is handing up every once in while and that's just what the problem was.
Once I added the Marvel Mystery Oil I never had the problem again.
Crazy thing is it really felt like an electrical problem and it was not.
Great product with many uses and it really works. Jimbo