I actually owned one of those just a little over 100 years ago. It was in a
DuBro (yes) helicopter. It was about the poorest running thing I've ever seen.
Could very well have been my fault as well as the engines back then. As I
recall you saw them primarily in boats at the time. Seems like they were somewhere
in the neighborhood of 1-2 ci but not much power by todays standards. I certainly
wouldn't think it would be worth much but you never know.