OK, i'm getting there now, with the aircon pump and p/s removed, there will be no suitable pulley for the belt to loop round, allowing the plane side of the belt to engage the water pump in the right direction. the little pulley to the left and below the alternator is damaged (on my photo above), but could be replaced, and then needs to be remounted above and to the right of the water pump. such as this:

the confusion over the water pump, seems to be you can swap it for an earlier version rotating the right way on a silver top, but this won't fit a black top. u.s water pumps seems too much hassle for me.