Let me tell you a story about Champion plugs and the H260 Continental:
1985: Built my first H260 engine(stock rebuild) and put a good 4 hours on the engine (and the D16 champion plugs) before the first pull. On the 2nd hook, I fouled 2 of the 4 plugs at the 75ft mark. Took it home and pulled those things out and installed AC C86 plugs. Ran those AC plugs for 4 years until I tore the engine down to modify.
Now I have heard people say that the D16 plug is too cold for pulling. I have also learned in the meantime that the way Champion "rates" their heat range versus everyone else is a little off. Much like a D21 Champion is the actual equivalent of an AC C86 (not the C88).
Fast forward 26 years (2011), I purchased a set of D21 Champion plugs thinking that SURELY CHAMPION HAS SOLVED ANY PROBLEMS THEY MAY HAVE HAD IN 25+ YEARS!!!!! Installed these plugs in a 500+ cubic inch engine, took it to the dyno to tune it, and fouled out 2 of the 4 plugs within a few minutes of dyno work. Removed those POS and installed Autolite 386 plugs and am still running them today.
Some people may say that spark plugs are like oil, but you could not give me a set of Champion plugs and/or give me enough money to install them in a Massey 44.