[Bruce]

I used the water inlet casting that Scalded Dog sells. It has a boss that is tapped for the temp probe. It makes a neat application, but it measures the water temperature as it leaves the radiator. Splicing the probe pipe into the water outlet hose (top of head to top of radiator) takes a lot of flex out of that connection. It also complicates use of a thermost -- if you are a believer. Some of the vendors sell an outlet that has a cast boss that is tapped for the probe. But the problem of routing the sender wire remains. It is very difficult to hide. That said, the exit mount does measure the temperature of the coolant when it is exiting the engine, which MAY be a more accurate read.
I did see a very neat setup at the Illinois Region's recent swap meet. Vince Scalabrino (I think it was on his table) had a short tube that was tapped internally and threaded externally with a set of precision jam nuts that squeeze tight in a hole drilled right into the radiator hose. The probe treaded into the fitting. It was a very neat deal, but you'd still have to route the wire along the top of the head from front to back of the engine.