Do I have the wrong spark plugs installed?

[Zappafan]

I finally got around to updating my spark plug wires and while doing so, pulled a few plugs to see what condition they were in. They are NGK5ES. I don't see this plug listed for my truck, 1964 1500 with 305 v6. They seem to work fine, but were quite black. I put this down to the previous owner having a really bad carb setup on the engine when I bought it. Is there an NGK that people are using in these older engines? I always ran AC's years ago when I had Pontiacs and never had an issue with them.