Hi there
from what I can recall the top
window on the 580BT is a one piece window; however the two piece opening window from a 580C should fit straight in to your machine.
If your machine has already been fitted with a two piece window then it should push outwards, please note that sometimes the mechanism can stick with age so I would suggest carefully spraying the mechanism with a good quality freeing agent like WD40.
Hope that helps.
Jeremy