Miles? This happened 15 minutes after start up during break in. That's when I started hearing it. And yes, the lifters rotate smoothly in their bores. Nothing wrong with any of the original AMC equipment I am working with. Perhaps I didn't inspect all the cam lobes as carefully as I should have.
What I think it boils down to, is there are a lot of seconds and perhaps rejected parts that get re-boxed and put back up for sale by vendors all over the country. When it says "last one", that should be a clear indicator. This cam kit wasn't marked as such, but it was the only one I could find available without waiting another month and a half.
No worries, I'm 70% there.