The built: a scale model of the russian 203 mm howitzer
The tracks on the gun come from a kit bought at a dollar store. The backhoe kit was at the right scale and a used the tracks to built the gun. Eventhough, I hadn't any scale drawing, the rest of the work was pretty easy to do. I think the overal result is quite good.
For more détails (in french) , please Petite Infanterie blog