So the pulley is keyed to the shaft, and has two flats on its inboard side so you can hold it with a spanner while you undo the retaining nut on its outboard side. That means the pulley is drawn onto the shaft as far as possible, until it hits a shoulder on its inboard side. Since the inboard end of the pulley is just about up against the shaft bearing (attached to the side plate) the lateral position of the top pulley has to be right. And the two idler pulleys seem to line up with the top pulley, they just don't line up with the bottom pulley. And the problem with the bottom pulley's location may be that the reel's axle shaft is out of position: too far toward the pulley side of the mower. I don't know what is causing that, but it probably needs to be lifted out and its components and their sequence compared with the illustration. I can't tell if Component 148, Cutter Pulley, has something inappropriate on its inboard side or not - from the illustration I don't think there should be anything between it and the inner ring of the reel bearing.
