If you looked at the articles on landships.info you would have found:
Landships II
A further exploration would have given you:
Saint-Chamond SPGs
Landships II
You are, I believe, referring to the Holt Mark VII SPG (3inch M1916 gun) which was made in Stockton. Most of the other Holt SPGs were made in the Rock Island Arsenal.
Landships II
There were also Christie SPGs - built before his series of tanks.
Landships II
The "huge" tank may be the steam tank built by the US Army Corps of Engineers in 1918. Unfortunately there are no drawings of the tank or sufficiently detailed images to create decent drawings.
Landships II
It is possible to turn a .stl file into a papermodel using Blender. I have a really good Dicke Berta .stl model on Landships II. Look in 3D Models. Now that would be challenge - and I'd host the resulting papermodel on Landships...
Regards,
Charlie