I so love that you asked this question. A baking/stewing hen is the ticket to the best chicken and dumplings you will ever have. That said, finding a good stewing hen today is not as easy as it was years ago.
Let me give you a little info on this. I've referred to my mother many times in my questions and answers. She was born in 1913 and would be 101 years old if she were here today. She would never consider making chicken and dumplings except with a stewing hen. So, that was the taste I grew up with.
Back years ago chickens were not bred like they are today. You could tell a baking or stewing hen by its weight which correlated to it being an older chicken. You would always look for a chicken that was 5 pounds or more. (Back then fryers weighed in a 2-1/2 to 3 pound max.)
Nowadays chickens that are sold to consumers like you and me are bred and raised to grow at a faster rate so they are much larger at a younger age. (Less time, less cost.) So, it's not uncommon to find a fryer that weighs over 4 pounds. (Note that foodservice still seems to distribute the smaller birds. Think about the prepared rotisserie chickens sold in grocery stores. They are usually barely over two pounds!)
Another thing to consider is chicken parts. Back years ago, chicken thighs weighed approximately 3 ounces each. Today, what you buy typically averages 6 to 8 ounces per piece. Let's upsize! They are capitalizing on the number of pieces rather than the weight. It's not that hard to figure out.
As I grew older I thought that a larger chicken related to a good result. Not so. The results from a large, quickly raised fryer will not give you the same taste as an older chicken.
If you really have a baking/stewing hen, regardless of the weight, you will have a lot of grease cooking out. Ladle it off. The flavor is definitely worth it. I don't think the weight matters as much today as it used to because of how it is raised to be sold to us. I have still found good frozen baking/stewing hens in the 5-6 pound range.
I can't speak to the specific birds you have, but definitely give them a go. If you really have baking/stewing hens you will be pleasantly delighted.
Just a note - My husband didn't think it made a lot of difference until I actually found a stewing chicken and made chicken and dumplings with it. He's definitely a believer now!