I believe it may have to do with the assembly number of the driveshaft. Post (or article) I read years ago and probably have it filed someplace.
Again do not quote me on this. It may have been sonething aboiut the yokes at each end. i.e. trac pac behind an auto vs 4 speed
a non hemi / 440 was spec'ed for a dana may have required different rear yoke?
What was the tail shaft you have from?
That image is from an online magazine and not mine. I’m rebuilding my 727 and I’d like to learn more about inspection marks, numbers, etc. Here is another from a member on here:
