It's been awhile since I had to pull off a power steering pump, so forgive me I forget the thread size, but I think it is something like 3/8" x 18, but don't quote me on that, check 1st.
Here is a tool that I have had for years for the install and removal of the power steering pump pulley.
you can install it with no special tools, believe it or not. You just need a long bolt (about 3" and at least grade 5, a nut and a washer, that is basically what the installation tool is. Chase the threads in the pump so that they are useable first.
The long bolt on the bottom left of the kit is one that comes from a new pump, nothing special. Basically the bolt nut and washer are a makeshift press to "press" the pulley back on
- spin the nut onto the bolt and slide the washer on
- insert the pulley onto the pump, loosely then insert the bolt onto the pump, then tighten bolt
- make sure the bolt is spun in with good contact with enough threads engaged
- with a wrench, start turning nut to tighten pulley onto pump while at the same time holding the bolt still with another wrench or socket, you may have to fiddle with the alignment at 1st, but make sure the pulley is square with the pump before tightening all the way.
- once the pulley is on and set, remove bolt nut and washer.