I think I might have worked around it. My app needed qt-4.x-base.tcz, which I got from your link, and also libpng.tcz. However, 5.1 already has libpng, so i renamed the libpng from the older version, included the renamed one and the app runs. I was missing lib12.so.0. the new libpng has lib16* files, so maybe there's no overlap.
Did I get out of jail?