The pump you have looks like it needs the 7" pulley. The earlier pumps use about a 4.25" pulley but the later uses a 7" version.
Just to make sure I have to ask: Does your current pump have round fins that sit "inside" the block? It loks like a round circle and there is a matching big round hole on the front of the block. The old version doesn't have a big hole as the pump mounts on the outside front of the block. Look at this picture:
water pumps The pump on the left is the later version and looks like yours.
