Gun Carriers were probably the first true self-propelled guns, writes historian David Fletcher
No example of a Gun Carrier Machine has survived since the Imperial War Museum scrapped their example at the Crystal Palace between the wars. However, the Imperial War Museum has a beautiful scale model.
Made by the model engineers Twinings, it appears to be perfect in every visible detail, so that will do as a prototype in this case. Failing that, the two types of gun that it could carry do survive if you know where to look. A 60-pounder Mark I was on display in the Imperial War Museum, and there is one in Canada, among other locations, while a 6in howitzer of the right period exists in several places including South Africa.