" I wonder if my Pertronix module comment a few weeks earlier in another post (where I said that I heard Pertronix modules were trouble free once installed) came back to bite me."
I have never heard that Pertronix modules are "trouble free". I have heard about too many Pertronix modules going belly up to ever believe that in both Speedsters and Hot Rods. They truly are heat-soak sensitive and degrade at a premature rate, giving the same symptoms as you've seen, especially the weird tach. If you swap it out for a new one, get two and keep the other in the Frunk as a spare. They're easy to swap on the road - Done that a couple of times at Carlisle.
I would be REALLY surprised if it was the plugs or coil. The coil AND tach get their signals from the Pertronix.
I would NOT be surprised at all that the Pertronix module is toast.