Its virtually impossible to use a mechanical sender with the standard 1/2" NPT fitting before the thermostat. You could use a 3/8"-1/2" adapter, but itd set the probe substancially out of the coolant path. Since most electronic gauges are 3/8" NPT, so finding a descent spot for that isnt a problem. What I chose to do was weld the 1/2" fitting for the mech gauge to the thermostat neck. This puts the probe just above the thermostat, but directly in the flow of coolant. I get quick and consistant readings there once the thermostat has opened. Until the car is warmed up, I just keep my eye on the OE gauge. Here is a picture of how I mounted my sender.
