You may want the s-10 tail section for another reason: It comes with a shifter box that is close to the main case as opposed to at the far end of the tail shaft. In the AD trucks if you use the z-28 tail shaft you'll end up with your shifter under your seat, or very close to it, I don't know if that is the same with your 67, but its worth thinking about.
When I was researching switching to a t-5 in my '51 I read a posting that talked about using a World Class T-5 box, which has nicer bearings a better gear ratios (like the z-28 tranny), and the tail shaft from an earlier one for the two reasons you need to do it: speedo gear and shifter box. The posting even has pictures! Try the 'search' function on this site and inliners for the t-5 conversion and read some of the articles in 2005, like this one:
http://www.inliners.org/Jack/T5tech.html Here's another website with info and a source for T-5 parts:
http://www.5speeds.com/t5/
