Check this out. A web page selling a restored reproduction of a single side-view patent drawing of christies SPG. However, it is only one restored image of a total of 7 figures for that patent.
Listed at the bottom of the page is Christies maddeningly extensive explanation of his vehicle relating to the 7 diagrams in the patent. My question is, where are the rest of his diagram figures? With this information, and his notations, one could make an -exact- model of this thing. And here I was thinking this vehicle could never be made in model form for lack of information!
And, if you look at his notes, this thing wasn't specifically designed as a SPG. It was designed as a cargo hauler, dirigible tender, and other such tasks. Like most of Christies tracked vehicles, this one was meant to run on track or wheel. As I understand it, it was completed in 1918, although these patents were for 1920.
Click on 'Quick Search'; type 'Walter Christie' in 'search terms', remembering to tick 'Persons or organisations' in the box above. You will get 6 pages of patents (there are 55 by various Christies); Walter's tanks and SPGs, of which there are a lot of patents (usually labelled 'tractor' or 'No English title available'), are on pages 4 to 6. Patents can be downloaded free as pdf files, just follow the instructions when you get there. The other patent drawings you link to can be found here as well.
This is the 'weird SPG' (click the 'original document' tab):
Here, I've copied the drawing from the front page (of ten, 4 of which contain detailed drawings) and rotated it in Photoshop, to give an idea of the quality:
They print superbly from laserprinters. You would, of course, have to use the drawings in conjunction with photos of the vehicle, as there are detail differences. Nevertheless, the patent drawings are surprisingly close to the actual vehicle as built.