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>The 205 has a cast iron case
>and the 203 has an aluminum
>case generally the 205 is said
>to be much stronger and more
>desirable
The 203 is cast iron case as well with the possibility of an aluminum tall housing. If the transfer case is all aluminum, it is more likely a NP208 which has a better low range gear ratio than the 203 or the 205. (2.61:1 vs 2.00:1)
Both the 203 and the 205 are cast iron. The 203 is a chain drive unit. The easiest way to tell if it is a 205 is to look for a round (about 1 1/2"), 3 bolt cover on the back. If it has one, its the 205.
For what its worth, I had my transfer case out about a year ago. While it was out I decided to clean it up and found a nice looking blue colored id tag. The transfer case itself was cast iron and heavy as hell, took me and a buddy and two jacks to pull it and put it back in. Anyhow, I remember the stamping on the tag being such that I couldn't read if it was a 203 or a 208. At the time I didn't know that there were two transfer cases that were coincidently 203 and 208; I just remember not being able to tell whether that last digit was a 3 or an 8. Guess this doesn't help much, point being the tag isn't a sure thing.