Home brew cargo bike

I saw this homemade cargo bike parked in harvard sq and later on the Memorial  drive path.  I've seen instructions for this kind of diy cargo bike via bike Portland from a bike hacker, but it's one of those things that requires a welding rig, and I'm just not quite that hardcore. Yet.  

I aspire to someday own a bakfiets and I wonder how this system works. I hope to see the guy with his bike sometime so I can ask for more details.  The Scientist just wants to know what's in the box