The only diagrams I've seen are in older posts in this "DSII only" section of the forum. And then there's Roger's book (but I don't have a copy because I don't own a DSII).
Is there any indication how the downhaul was/is supposed to be rigged in your boat?
I've sailed on a DS II for a few days, and don't recall that overhead purchase, but can't remember how the downhaul was rigged. I have one not very clear photo that boat's cuddy with the doors open and there's clearly no vertical purchase visible, but nothing that shows the forward end of the CB. (I checked, the owner posted a picture only of the uphaul)
I take it you don't have the setup like it's diagrammed here:
viewtopic.php?f=2&t=4944&p=26393