NP203 is mostly cast iron. It does have a big aluminum section and they are extremely heavy. Part time kits are available and many people use them in conjunction with the 205 to create a "doubler" for crawling.
Southern Rebel, I would guess that your truck has a Dana20.
Here's some pics of my NP203 when I pulled my transmission:
http://info.imageink.com/chris/image026.jpg
http://info.imageink.com/chris/image028.jpg