I have a 1961 A-4 that I've recently converted to fresh water cooling, electronic ignition, etc. and the sending unit for the temperature gauge is fitted into a bronze tee that comes off the back of the exhaust manifold, where the cooling water exits the engine. The manifold is tapped for 1/2" pipe thread and you can replace whatever fitting you have with a short pipe nipple and the tee. Works just fine for me.

Eric