What were the dimensions of this gun? Specifically, I need to know the height, the width, and the length of the entire piece, not just the barrel.
I found a site with extensive information about the cannon. It includes beautiful scale drawings. While they do not include the height and width explicitly, they do have the total length of the cannon (2.5m) which can be used to extrapolate the scale of the images in pixels / cm. Pixels are used because they will not change with your screen or zoom.
In the first image the cannon is about 700 pixels long giving 2.8 pixels / cm. In the second it is about 370 pixels long giving about 1.5 pixels / cm. These are rough measurements.
If that is not enough, the piece is located at the Musee de L'artillerie in Draguignan, France. That link includes a phone number you can call. The curator may oblige to measure it for you.