Metal mixing in XJS cooling system

OK, I think I found a place for my aftermarket temp sensor
without tapping, dieing, drilling, etc. My car has a metal
elbow in the bottom radiator hose with a fitting for
plugging the car up. I suppose this is a cold weather
climate option. Anyway since I live in S.A. Texas I can't see
much use for it. Therefore, I've found a replacement bushing
with a reduction to the 3/8" input my sensor needs that may
work perfectly. Two questions though, 1, I think the elbow
is aluminum, the sensor is brass and the bushing (from local
hardware) is galvanized steel. Is this metal corrosion
disaster?? Next, is locating a temp sensor to control my big
fan in the lower radiator hose a good or bad idea? Thanks
for any help. I'm ready to get this car back on the road!!
Thanks again,
Don
1994 XJS Coupe, 6.0L