Allen, it probably has the 4.56 gears. Unless you want to stay totally original, you might want to consider switching to 4.10 gears. As mentioned above, the center section is an easy, direct swap out. It is a particularly easy swap with the rear end out of the truck because you don't have to do it laying on your back! The 4.10 will give you much better gearing for today's roads.
There is one for sale in the swap meet forum.
If you want to look for one locally, keep your eyes open for 1967 to 1972 C20's and C30's with V8's and automatics.
Matt
