The woodruff key has a round bottom, like a half-moon. You should be able to support the shaft from below with a piece of brass or something, and a good steel punch to drive down one end of the woodruff key. That would lever the other end up and out, working it loose. Might need to work both sides of the key, but that should get it moving for you.
Swapping out the shaft is a full injection pump rebuild.
Swapping out the shaft is a full injection pump rebuild.