I made a 900 mile round trip in my SBC powered A. In the course of the trip, it developed a cylinder miss. After getting home, tested header exhaust port temperatures and found low on only #1. Swapped plug wire and examined spark plug appearance. No change in engine beat after refiring to listen and measure temps. Distributor cap is garden variety black plastic with aluminum ......dadgummit....terminals to send spark. Moroso fat plug wires. 9.25 compression. R45TS plugs with .040 gap. GM point distributor with Crane electronic conversion. MSD coil. Crane whatever box that mimics and MSD to a point. 2200 lb car with stick and 3.50 gear. This is the question. Am I killing the plug wires or distributor cap with plug gap? The ignition box and coil are going to provide what they do based on resistance as spark plugs also do. Plug gap based on what I thought was correct made me change from .035 gap to .040. The engine beat got stronger based on that experiment and a few thousand miles. I wonder if the cam is going flat at #1, but the sound of the mechanical aspect doesn't sound that way. I would think a significant clatter would develop if that was the story, could be wrong, haven't pulled the valve cover to measure valve/rocker movement differences if there. Exhaust temp heat with engine running at header port is 260 area except #1. It is many degrees low, 140. I don't think I want to know the answer, but it needs to be fixed. My cheapest best guess is distributor cap, could be wrong.