Spark Plug Heat Range

In 1965 I had a 63 dodge 330. We changed the pistons to the 13.5:1 ratio ones and had spark plug problems. We got fuel from the airport and the problem persisted, little beads on the porcelain. Also porcelain very white and glazed. The only solution we could get then was J2J Champion spark plugs which worked great. The originals were J9Y Champions. I don't remember exactly what J2J's fit, a 2 stroke lawn mower I think. We just couldn't find any of the "racing" plugs, different numbering system, where I lived. Anchient history huh?