I don't see an issue with DLS increasing net debt position from...

I don't see an issue with DLS increasing net debt position from about nil today to 200-300m net debt for a buy like this. Issue with CB assets of JV is that they are cash hungry for any change in production levels. The SACB JV recently ploughed lots of cash in (see bpt evolution of net debt) with mixed results. If these assets are cash positive for DLS over the horizon then, with the benefit of owning part of the CB infrastructure, I would definitely consider them.
Origin had little else in the CB so selling the CB assets to someone who can leverage these assets makes sense.