I can confirm that Series V transmissions came with 10 spline first, and then later changed to fine spline. However, I was once specifically told by someone who I figured would know that all all-sychro OD's had fine spline in front and 10 spline in back. I wonder if he was wrong, or your transmission had a changed first motion shaft.
I also seem to recall that the fine spline transmission had slightly different ratios. Can anyone confirm that?
Jay '67 Bentbeam