Thanks for the suggestions folks. I put a magnet on it, and it's definitely NOT cast iron, as the magnet doesn't stick. Guess that makes it aluminum. I assumed it wasn't CI because it just doesn't have the weight that CI pieces of that size do.
The pan measures about 21" long on the top including the handles and 9-3/8" wide. The bottom part that's recessed measures about 16-3/4" long and 7" wide. Those dimensions would seem to fit the theory that this would have fit into two stove openings with the center removed, especially given the round ends.
Perry, I'll send you a note, When I had the surgery, I figured out I couldn't afford to collect, but I enjoy finding and restoring so much that the next best thing is selling them. I think I love the hunt more than owning them--just the way I'm built.
The number two Griswold came out of the lye bath over the weekend--beautiful and won't need the electro. I have to decide whether I want to season it or sell it the way it is. I'll post pics this week.
Also found a number 8 Wagner Ware National over the weekend--first one I've ever seen in person. Needs some work, but it'll be worth it.