DAVE TOTZKE - Replacing the inner rod in a lift lever can be done, but finding a replacement rock shaft is probably easier unless you have a pretty well equipped shop.
Carefully remove the rockshaft from the tractor like Tom H said, and remove the rest of the inner rod, it will come out the bottom of the lift lever but will bend when it hits the rockshaft, you'll have to straighten it out to get the correct length of the replacement inner rod you'll be making. I'd get the new top button, spring, & washer from one of the sponsors here, and carefully measure the whole length of the inner rod including the bent end on the bottom and the twisted off threaded end on top. Then get a 3 ft length of the same diameter rod from a hardware store, I forget if it's 5/16" or 3/8", cut it to length, cut threads on the top end so the buttom screws on, and install the washer & spring, then the button. Feed the new rod you made down from the top of the lift lever and clamp it some how so it stays extended out the bottom, small pair of vice-grips on the bottoom works. Then you have to HEAT & BEND the bottom end so it can engage the slots in the quadrant on the bottom. I have an acetylene torch so I used that to heat the rod red hot, but a MAPP gas torch might work, I tried a propane torch and it wasn't hot enough. I drilled a hole in a piece of 1/2" dia round bar the same depth as the length of the bent end, then heated the new rod, slid the drilled 1/2" rod over the new inner rod and bent it. Keep in mind you're working with red hot steel, it'll burn you if you're not careful.
The first time I tried to replace the inner rod I tried pushing it up from below and it bends the new inner rod when it hits the rockshaft and starts into the lift lever and the new rod will stick, so don't waste your time trying it that way.
The parts books from when these old NF tractors were new show that inner rod was "NLA", meaning you can't simply replace it with a new inner rod because it was part of a complete assembly welded in a jig by IH. The inner rod was installed prior to welding the left lever to the rockshaft, but it CAN be replaced. I went thru that all about 10-12 yrs ago on my CC #72 and my replacement inner rod has worked great.