Flyingmonk wrote:
What would you consider a modern engine?

In this case, something you could put a big reduction gear on since
you want to slowly turn a big prop.

Specialized manufacturers of Hollywood lighting generators used
rebuilt flathead Cadillac V8s for decades because when properly rebuilt
they were the quietest engines they could find. Power-to-weight might
be problematic for aircraft use though. And in no way modern.