I did a conversion on my 1772 and kept the original gauge installed under the hood along with the hour meter just to make sure they read the same.
IIRC, you won't find anything that will fit into the original sending unit location.
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I purchased a gooseneck(what I call it) from Rich Patton off of a 1782/2182 that has the sending unit port on the engine side of the thermostat & water pump. This will give you a true reading of the circulated water temp inside the engine. This will give you the room to mount any type of mechanical sending unit.
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I purchased this set of gauges from O'Reilly Auto Parts.
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But you will have a problem with the clearance on the back.
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I made a spacer to get the clearance I needed.
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The gauge reads the same as the original gauge that is still mounted under the hood and so far I have had no problem.
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