At Bonneville in 79 a Champion rep gave me a bunch of plugs for my GMC powered altered. I don't have the Jimmy any more, but I do have several plugs. Three boxes of ten new J6C plugs, Three J79s and a half dozen or so J6cs that were used for warm up. I don't know but I bet they fit flatheads and Chevys and lots of early and later 50s engines. 14 MM thread with 3/8 reach. $30 shipped to your door in the 48. If you need the same plug but with a 1/2 long thread, like for aluminum heads on a flathead Ford, I have 14 LG3 plugs. Used for three miles or so. There are a lot more plugs around here I need to look at. For BBFord and a bunch of 10mm plugs from my twin plug Plymouth 4.