How about a lifter that is haning up?
I had a very similar problem with my 350 where every once in a while it had a intermittent miss and I went through the plugs, wires, vacuum lines, distributor and a few other things trying to figure where it was.
Add one bottle of Marvel Mystery oil into the crankcase and see if the problem goes away.
For me that was all it took and I never had the problem again.
It feels just like an electrical problem and until a good friend mentioned the lifter I had never even thought about it.
Hope that helps Jimbo