I want to know what the temp is coming out of the engine. That's the temp that's critical in my opinion.
Many years ago I installed a slick temperature monitoring system in a 72 Datsun 240Z V8 conversion I did. I installed temperature sending units (drilled and tapped holes when needed) in the rear differential, transmission fluid and engine
oil. I ran wire and fed all the sending units up to a partially hidden 3 position rotary switch (Radio Shack sourced). The switch was mounted on a hand fabricated 0.064" thick aluminum "L" bracket, engraved with "eng", "trans" & "diff". It was sprayed semi-gloss black and screwed to the side of the tunnel. The gauge was fed from the installed rotary switch's output. It was nice to be able to switch between the various temps. If I recall the whole system ran me <50 bucks to build..