I would try a thread file and see if you can fix whats left. I would bet the end is mushroomed out from beating on trying to get the pitman arm off at some point. They then messed up the threads trying to back together. I just checked e-bay for 1955 truck pitman shaft, there is a NOS one for a reasonable price. Best to find the actual part number of what you have, http://chevy.oldcarmanualproject.com/1929_57chevyparts/index.htm