Reaching back a ways here is a custom built pedal powered side by side quadcycle featured on a local TV station.
Unfortunately the video quality is not very good, but you can get the general idea of what this man made so many years ago. I have no idea if it was the first side by side quad ever made.
Here is the video description:
From the VHS video library of Steven K. Roberts comes this local news report of a mid 80s built side by side quadcycle. According to the piece this was designed and build by Norm Ogle with help from Peter Johnson.
If I were a younger man and not having the physical issues I have now in my elderly years I would be fabricating various tadpole trikes and quads. I made one tadpole trike back in 2007 and I was already challenged somewhat with vision problems then.
Lastly, my thanks to Gary Solomon of Laidback Bike Report for giving his permission to share this video from his YouTube channel.