Uh - you don't want to put the gauge sending unit in that location in the t'stat housing either. That puts it AFTER the t'stat. So, if the t'stat fails, and fails CLOSED as they often do, it's entirely possible that you won't get an indication of it in time to shut the car down -- because the high temp will be occuring on the OTHER side of the t'stat -- the sender will be sensing cooler temps than what's actually happening.
If you're gonna mount an aftermarket gauge guys, you need to put the sender where the factory sender went -- in the water passage in the intake near the #5 cylinder/runner.