I got my blight kings the other day, and I would disagree with the blight kings heads fitting. They look way smaller, and don't fit like a DG helmet that sits down into the neck. The BK heads fit onto a sided neck joint, so there's no back to the heads. While it might be possible to make a bare head swap or two with a lot of gs work, I don't think the work required might not be worth it. I'll take a couple of photos later for you.
Yeah you need to do a little GE work to make the connection but some of them work. The others do look to small. The nurgling-looking head and the bug looked the best.
Again, not a perfect fit but doesn't take a lot to make work.