[Alex V.]

There's certainly variety in plug choices. The only input I'll offer is that I've never seen a set of Autolite plugs that wasn't visibly eroded - even iridiums in calm modern car/van V6's, and they couldn't have all been 120K+ miles old. Which also coincides with the fact that they're usually one of the cheapest options in a given application. And that your leisurely six won't have any problem with good ol' copper plugs.