Converting the early 150 model to 180 hp is now available through Mike Horton of Lubbock, Texas. The STC allows for the o320 to be replace with the o360 A1A. The late Jeff Cloud had the arrangement in his tow plane and it was very good. No it is not a 235, nor should it be, but it is a very adequate tow plane. I believe that very Pawnee is still towing in Mass or somewhere up that way.
Mike Horton has assumed the ownership of the STC that is in his late fathers estate. The engine mount is from the Piper Commanche 180. I have spoken with Mike and he has a tremendous amount of information on the conversion.