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This wood box is intended as kitbash fodder for the MiniMetals 1941-1946 truck model. Its based on a real truck shown in a mid 1940s photo.
You will have to pry off the existing Mini Metals plastic body that comes with any of these truck models, exposing the frame. The frame should be shortened at the back end, as this box isn't quite as long. And you may choose to reduce the height of the frame (which I do by carving some off the top with a knife) to lower the box.
The cross pieces sprouting out on top of the box are not supposed to be part of the model. They are only there to ensure it is printed square and not bowed. They can be sipped off with sprue cutters and a little sanding with a sanding board to clean them up.