I know steering boxes are pretty easy to swap around and that there arent really that many differences between the saginaw boxes used in dozens of applications, but dont know if all the sector shafts are the same.

What I'm wondering is do the sector shafts use the same thread diameter and pitch on a YJ box and a dodge half ton box?

The reason I'm wondering is I want to use this steering box brace system (http://www.solidsteel.ca/Stabilizer.htm)

http://www.solidsteel.ca/images/102_0249.jpg

http://www.solidsteel.ca/images/102_0266.jpg

Where can you buy a sector shaft like that?? I would love to get one to make something like that also!

You should be fine. The only difference is between the power box and the manual ones. They have a different size sector but I can't think of any power box sectors being different in size.