Hello Bill,
See the picture at the bottom of the page on this link:
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0405.htmIt sounds to me like you are describing the pin locations for the drive shaft bushings. There were originally a front and a rear drive shaft bushing. In the earlier torque tubes there was a pin holding each of these in place and the pins were peened in place (Later torque tubes had press fit bushing and no pins/holes). The torque tube had a front bushing closest to the ball, then a rear bushing, then a seal behind the rear bushing.
I would guess that the bushings or seal went bad at some point and the bushings were replaced with an "okie" bushing. The okie bushing is a single longer bushing sometimes with a seal attached to the back. It is my understanding that these bushings were invented so that the bushings can be replaced with the rear axle still in the truck. With the "Okie' bushing a pin was probably only put in the front bearing spot as I don't think the okie bushing is long enough to reach the rear hole. If the rear hole is covered by the sleeve/ball I wouldnt worry about it. If the rear hole is open under the truck I would plug it so junk isnt getting down in the rear end (although maybe the original rear bushing/seal is pushed deeper into the torque tube blocking the direct path to the rear end)
