Hose clamps... You can kind of see them in the pic in this
post. This was when I had my small block in there, but it will be the same thing. It's too bad you can't get the valve with threaded fittings, but this works fine.
Edit: Oh, and I'm using #12 hose for the heater lines. I bought EZ Clip fittings with #10 threaded O-ring ends and #12 hose ends. They work well and fit over the heater control valve just fine.