I have not yet tried to undo the clamp assembly though now that I've had another look at the manual page you posted, I think I'll try to do so next time I'm down at the boat (probably Wednesday).

Near as I can tell, the clamp in the parts manual looks the same as the one I have, though the elbow I have (part #12) looks very different from the one shown in the manual. The angle on mine is less and the outlet diameter on mine is significantly larger than it looks like the one in the manual has. Also, the raw water inlet on mine is much larger than the one in the manual looks. I suspect that the elbow I have is from a different model Westerbeke.

Hopefully, I'll be able to reuse the gasket (part #8). I just looked it up and a new one will cost me another $30. The exhaust manifold to head gaskets (part #5) were only about $11 each when I bought them