After studying the few available pictures on the web and comparing them to the model above I come to the conclusion the turret is utterly wrong!
The modeler simply installed the gun tube of the howitzer and that's it. On the original the skate ring for the .50cal was removed and a fix point installed instead on the turret front, and the gunner seat changed from the left to the right side of the gun. Also the turret did not have the longitudinal strut.
I wish I could go to Aberdeen and take some photos of the prototype.