Originally posted by nor'easter:
... Has anybody used a Duraspark ignition with the small cap? Any crossfire/misfire issues ...
I would be surprised to hear of cross-firing caused by the smaller diameter cap. As long as the engine is in a good state of tune, and the plugs and ignition wires are in good condition it shouldn't be a concern. The ignition shall only “cross-fire” when doing so provides a path to ground that is easier to travel than following the proper path to ground would be. When these ignitions were new they were igniting some very lean air/fuel mixtures diluted with exhaust gas (EGR), thus the engineers were rightfully concerned about cross-firing. If your engine is equipped with a carburetor or fuel injection system providing a better air/fuel mixture, and/or if the EGR has been misplaced sometime during the last 40 years, the concern for cross-firing is greatly reduced.
The 1976 Ford breakerless ignition was basically the same ignition as the 1977 Duraspark II ignition, yet it was factory equipped with a 4 inch cap (made from a new blue material that was supposedly more high voltage resistant).
Here's an excerpt of the Cleveland Symphony, performing "The Charge of the Rhino", for your entertainment on a Tuesday evening: