If I buy an AC Delco power steering pump does my new pulley need to be AC Delco as well?

It doesn't have to be a Delco part, but it does have to match the OE part in terms of size and design. Normally you would just press the old one off and then on the new pump. Did yours vanish when it broke?
As the pump seized up you are likely going to need a few other parts to keep a new pump happy, normally any warranty on a new pump will need a filter installed in the return line and a new reservoir or at least a cleaned one. The main issue is to determine what failed and did it send any debris into the steering rack. That is the idea of the filter. As for replacing it, remove the belt (as you had the pump seize, if the belt didn't break replace it and the tensioner. Then it's a matter of removing the lines, then the bolts and the pump.
If you get the replacement pump without a pulley you will need the pulley installation tool and a replacement center bolt if yours went with the pulley.