The 203 as it came from the factory was a great box.
When the part time kits were installed, most of them caused the oil pump to stop working.
Unless the thing is run in 4x4 regularly there are parts that dont get lubed.
As mentioned, the twin stick setup is really good.
The 203 has two levers on the case one is for the Range section and the other is the Lockup.
With the twin stick setup you can control the lockup section separately from the range.
The 203 was a really nice setup as it allowed for all wheel drive all the time.
Many times you dont need to touch anything, just drive the thing.
As was mentioned this box acts like an open differential in so much as the power flows to both front and back equally until one wheel loses traction.
The wheel without traction will spin and the rest will not receive any power until the lockup is activated.
GM, Ford and Dodge used the 203 in the Early to late 70's
The 203 and its cousin the 205 were tough as nails and really hard to break.
Now this said, out in the bush with a heavy foot, anything can be broken
Snowy