Block and Tackle Replacement

I'm assisting my father with finding a replacement block and tackle for a window he's installing. Unfortunately, the windows were out in the weather for quite a while so the springs have rusted and one broke. I have attached photos of the block and tackle that is not broken and the stamp on the side of it. The other photos are of the plastic piece in the channel of the window and the two ends of the block and tackle. The ends look nothing like what I've found online so I'm have a tough time. The string end is attached to the top of of the channel by a screw through the small metal plate.