Jan brings up a good point...I don't mind a larger base and boiler!
I am looking for a diminutive (small) main flywheel/cyl/rod assembly.
Another thought...I specified "double acting" but I would not mind if the piston is only steam powered in one direction, it "seems" like many small Ocillator type engines are single acting...it is the "Ocillator" style I am avoiding right now...I may collect them in the future as I become more knowledgeable about our hobby, but for now I prefure the steam cyl bore to remain fixed and not wobble as the piston travels thru it...I am not sure if there are any fixed cyl type that only power stroke one direction and let's the flywheel carry it back to next power stoke...put I suppose it is a possibility?
So diminutive flywheel/cyl/rod and quality is what I seek...hope this helps! I am going to go look at Jensen 35 now...I don't prefure boiler mount...but If I can remove assembly and remount on base...that is fine...I do enjoy modify things and personalize to my own taste, as long as it is not a high value collectors item!