You will need the following files from the original model:
Assembly instructions are exactly the same as the original. I recommend supports on the box body (regular supports in the slot). Note that because the arms are longer, you'll have to fit the lid on one side at a time (like slotting a battery into place).
If you want to edit the SCAD files, you'll need the other three models from the original model as well.
The author remixed this model.