My 1985 AC Delco catalog lists the 63-69 230 truck engine using R46N orR45XL spark plugs. 46 is one step hotter of a plug, good for oil burners or rich running.
Ebay has a ton of the green stripe R46N plugs, I have no problem buying NOS plugs. The pictures don't show 3/8" length, not sure where that came from, they look to be about 3/4' long.
