The function of a stock 203 is well described above. There are/were many companies that sold "part time conversion kits" for the 203 and therefore a lot of these trucks running around with converted 203's that allow 2wd.
In my opinion the 203 got a bad rap. Everybody says how horrible the full-time 4wd function of it was, but then look at all of the full-time 4wd vehicles on the market through the '90's to current.
I grew up in a farming community and when I was a kid it seemed like everybody had a late-70's Chevy K20 with a 203 t-case. Granted, they would wear out the u-joints on the front driveshafts but not any faster than the rear driveshaft joints so I guess they did cause more wear than a part-time truck. They did have better traction in the regular 4 hi mode than a 2wd truck as the farmers were alway pulling wagons out of fields. Still remember my older cousin who I helped bale hay through high school. They had an old '79 with the 203 and a new "at the time" '88. They never touched the t-case lever on the '79 but almost always had to shift into 4wd on the '88 to pull wagons out of the field. The 4-low unlocked position was really nice to for pulling really heavy wagons out on the road.
