Welcome to the forum Dennis,
You've given us a hard question. Not many of these boat anchors (they're HEAVY) are around so not too many to compare from.
Are the handles on your griddle open or closed with a small hole in one end? The open handle is the earlier one I would think from looking at other griddles in the red and blue books. Griswold may not have changed the No.11 griddle pattern as often as they did with the larger production smaller griddles so an older design may have been made later than for the smaller griddles. If your griddle has the solid type handles I would venture to guess it is later than the one with the reinforcing ribs. I say this because the later block TM long griddles have no reinforcing on the bottom while the earlier diamond TM No.7 griddle (blue book p. 58 center) does have the rinforcing. This is only a guess and not for certain. The date for your pan could be anywhere from c.1909 to c. mid20's or even later. Again, a guess due to the fact that No.11 griddles are so uncommon. I've never owned one for fear that my house would collapse and my stove wouldn't hold it. Value? Don't know at all.
Steve
PS I modified your profile so your real name appears on your post. That's required so we all know who we are talking to.
