Complex sentence: Therefore, the producers and their advisors decided to assemble a simulated steam train that was, instead, pushed from behind by an available diesel locomotive, which was directly behind the steam locomotive and disguised as a box car.
Split into simpler sentences: Therefore, the producers and their advisors decided to assemble a simulated steam train that was, instead, pushed from behind by an available diesel locomotive. It was coupled directly behind the steam locomotive and disguised as a box car.