Lewtot, yes there was a chevy in the '70s that used the plug. I had one and said I did in my first post. 3/8, tapered seat, short reach, 5/8" plug wrench.

Autolite 25 is one of those plugs. AC CR43TS is another, one I could find a jpeg for.

Before I posted I went to Rockauto and looked it up. Where did you get your information?

R.