That is definitely a New Process-203 transfer case.
There is (I forgot this earlier) an identification tag riveted on the front of the same housing between the range box and the front driveshaft that would have identified it also.
In the pic where the screw in plug is between the rear drive yoke housing and the front drive cover plate is, this is used for filling the transfer case with 80 weight gear lube, the 205 would have an intermediate shaft cover plate with three bolts there.
Does this truck have locking hubs? If so- then sometime in the past someone has installed a part time conversion kit. I won't get into that right now, but it's not really a bad thing to do to this transfer case.
Whick axles does this truck have? The front can either be a Dana 44, or a GM corporate 8.5 inch 10-bolt, and the rear SHOULD be the 8.875 inch 12-bolt.
As far as gears go you could have 3.08, 3.55, or 3.73's, and possibly some other ratio. Those are just the most common.