The main changes noted here for the existing models was an extended wheelbase for both models and the 57" track for the 150 model. It looked like the engineers were interested in getting more power to the 170 model with a V8 engine ans new style transfer case.
All these ideas came from a brochure dated (10/57) called "1958 Projects - Product Engineering" and highlighted some of the future options for Forward Control trucks. Only some of these items made it all the way through to the production floor. Many thanks to Paul Barry from Willys America for supplying this information.