Here's a link to Tom Langdon's store, showing plugs for HEI.

http://www.langdonsstovebolt.com/store/online-catalog/#!/Spark-Plug-Large-Gap-for-HEI-For-216-235-261-and-Mopar/p/37315489/category=361515


It's easier to get forgiveness than permission!
1946 1/2-Ton Chevy
1953 Chevy 3/4-ton Factory Stakebed