Got fuel, spark, comp but no start

I always start with the basics. My son has a 5.9 (Magnum) Dakota R/T and a few years ago it wouldn't start during the winter.
First day, I go over there, check a few things and couldn't get it to fire. (unheated apartment garage below 20* F)
Second day, I stopped at a parts store on the way over and got a new set of Champion plugs per the book.
Pulled the Autolites out that were in there and compared side-to-side to the new Champions the reach on the Autolites was much shorter.
Put the new plugs in and...instant start. The Autolites were recommended on the Dakota R/T club site and that's what he had bought a few months earlier but the electrode was short of the combustion chamber.