Kurt: thank you for the information. The Tankograd book covers the weapons system over its history and I have noted differences beyond the obvious which makes me question if there are differences in the real weapon over its changes from the easily observed differences. That said this is a nice model to build and better detailed than the Trumpeter offering.
Dark: the limber is present in the photo as I can just see part of the wheel. I do not believe this model can be set up as a towed piece/