The back was completely missing and there are no photos showing what it originally looked like but it was suggested that it was loosely based on a Jowett Bradford van, and there are some good photos online of the backs of those showing 2 windows, so I based it on that.
Below is the video of the restoration, including it actually working, but here's the before and after:


And the video:
https://youtu.be/n9h07tOAiY4