A couple reasons come to mind why it was not practical. First, if it weighed 350 pounds or so more than the OX5, the weight and balance had to be way off and very unstable. Also, it is very cold at altitude and all that exhaust steam would freeze on the airframe.....not a good thing for airplanes.
Some years ago Bill Lear of Lear Jet fame tried to develope a steam powered bus. He threw tons of money at the project and it never proved practical. If you can't make it work in a bus an airplane is a much greater problem.
Dan Markoff