Trans lines connect differently. 96 has both up front at the bellhousing, 97 has outlet in front and return in the middle. The converters may also be different. 97 was a changeover year. I know 96 5.7l gas engine will be a mid stall converter with a dual stator(specially built for the TBI engines), but in 96 GM realized the vortec didn't need the more expensive dual stator converter, and in 97 switched to a high stall cheaper single stator converter. As far as mechanically goes they're pretty different, but electrically they operate the same, and can be interchanged if you adapt the lines correctly.
