here is an engine similar in size to yours, ( 3/4" x 2 1/4"); the pot boiler is a copper tube 1.5" dia and 4" long...heated by an alcohol burner with 3 wicks. wheather was cold in my garage, hence the steam everywhere!
https://photos.app.goo.gl/qJ4x6SK8JqAM6ecu8
That is a lovely engine, and the music is a perfect choice for the background track!