ball and trunion to a splined output
if its an A body box with the ball and trunion,,its either a 1964 or 65 only,,as far as i know,,those boxes all have the 3.09 first gear,,and are not easy to come by,,, a 1966 box has a 2.66 first gear and 1970 and up has a 2.45 first gear,,with the exception od the OD BOXES they also have the 3.09 first gear,,
they also use the better side cover,,with the ball bearing detent,,,
the 3.09 will give you a little quicker RPM from a standing start,,,weather you convert the tail shaft or the yoke using the 4x4 stuff its worth it,, i have one that i converted the tail shaft,,the easiest way to do that is to get a junk donor trans,,make sure you get one withg the same size main shaft and bearings,,