Installing temp guage sensor(aftermarket)

Well, I mean no disrespect, but unless someone gives me a plausible reason WHY I shouldn't drill and tap the existing hole and mount the sensor in the most logical spot for it, here in a few days I'm gonna buy a 3/8 npt tap. I cherish this car but I'm more worried about it being functional than keeping it original.
Seriously, if you have a horror story, lay it on me and I'll go buy a T-fitting for the radiator hose. It just seems to me that the temp you're wanting to read is the motor itself.