You're going to need a press for the overdrive. The spring has about 800lbs of pressure on it and isn't anything you want to take lightly. They make a special tool to help make this easier that you can either buy or make. You'll want to use your intermediate shaft to line up all the splines down in there before you press it together. The shop I worked in had an old shaft cut down to leave in there while it was being pressed together. Made it a relatively simple process.
The valve body is a little more complicated, but if you're going to the trouble of rebuilding the rest then it should be completely disassembled and cleaned. I've seen guys throw new clutches and steels in just to have it go out again within months. They didn't do anything with the valve body and it put lots of trash in the transmission, as well as had sticking valves which caused the problem to happen again.
Replace your converter. Precision of New Hampton makes a great heavy duty unit that comes is a lower stall, has an anti-balloon ring, and can be ordered with a drain plug. Comes in handy when servicing the transmission.
If your truck is stock, then a relatively stock rebuild will probably work ok for you. If you have a bunch of mods then you'd probably be better off looking up someone who builds these for a living. There's a lot of tricks that can be done to help these last behind a Cummins.
