Frank Stelzer was a fine inventor, without any "formal" education. His motor, unlike many similar flights of fancy, actually works - with very low revs only. The motor is next to impossible to balance with the usual 2-cylinder configuration. And it vibrates like crazy.
It would be rather a simple modeling proposition, Stelzer´s own motors were just biggish models anyway.
Thanks for reminding me about an engine I had completely forgotten!