Bill

Right you are,  Bill.  I thought I caught that error, but I was wrong.  Error squared.   (Blush)

As for prop efficiency, without data, one can only guess.  As for unusual engine, if is a piston engine with a compression of around 8-9, use a specific fuel consumption of 0.39-0.40 pounds per HP hour  leaned for cruise, and use that. 

Cheap tests yield cheap results.  Better than none, but best we can do. 

Fred