There's a little confusion here. Seems that some of the info you've got is crossed up, as some of it actually applies to 1/2 tons, namely the 17 vs. 30 spline and the axle length issue. That would apply to the early 12 bolt, which changed spline in '65, and the '63-'70 6 lig vs. the '71-76 5 lug for the axle length.
To answer the question, the 3/4 and 1 ton 3rd member (pumkin, hogs head) will swap from the '47 model up to the '72 models. The desireable one would be the later '68-'72 which could be had with a 4.10 gear. There was at one time a 3.90 gear, and if you get REALLY LUCKY, there was a 3.54 only made in '72. The swap is a direct bolt in.
