On a serious note, assuming the ring issue could be solved I suspect the big issue would be seizures. A square piston is going to expand in strange ways and accommodating that will be difficult.
The guy correctly stated that the pistons need to be tapered, like normal pistons, but he didn’t mention that normal pistons are not round, they are actually oval.
The amount of taper and ovality is minor, and crucial.
In my mind square pistons complicate this topic by a huge factor.
And…
I gotta state the obvious, an ‘experiment’ is usually a hypothesis test (a controlled test to either prove or disprove the hypothesis).
This guys hypothesis was that he could make it run. Not run good, just run!
That is an inadequate hypothesis when we already have existing (round pistons) engines that run better than their inventors could have possibly imagined.
When we have good existing solutions, a sensible hypothesis has to be that it is IMPROVING upon existing designs in some way.
This ‘experiment’ didn’t solve any problems or improve upon what they already had.
Hence my earlier comment… dude got too much spare time on his hands !!