As you may know already, or soon will find out through research, Griswold made the Iron Mountain line in the 1940s as a line of a more economy grade cookware. As I've read, they were made to sell at a lower price than the marked Griswold's through hardware stores, etc. They had paper labels on them.
Everyone has their own tastes, but I think they're a great deal: Griswold quality, with some style in the handle design, but generally without the big Gris' prices, especially from unknowledgeable sellers.
For some reason, #5 skillets are mainly all we find in my area of Maine. I do have two Chicken pans, but sadly, no covers for them.
I don't know how to post a link to other sources. If you do a Google search under "Griswold Iron Mountain Cookware", you'll see that the third site in the listing is a series of posts through the "Wagner & Griswold Society Information" that discusses what's available in this line and includes a picture of an Iron Mountain label.