Nice find and no it hasn't been posted before, as google hasn't plagiarised the back issues of Mechanix Illustrated it's not easy to find out how many issues contain O&R articles.
Looks like the wheelbarrow, garden roller, cart, pedal car, lawnmower, cultivator & unicycle are all actually examples of possible uses for the 'Tiny Mite' powered wheel, which was made in eight, ten & twelve inch versions, with an optional extra fork or frame to use with equipment of your choice. They also sold the mini-scooter too.
Not sure I would like to try that unicycle at 17mph.
I wonder how they kept the two engines synchronised.
David