That's the same setup I have on a 1772. The D640 has the same type sending unit on the head as the D600. I purchased the water flange from Rich Patton. I think it was off of a newer Kubota WG engine. I kept the old temperature unit and mounted it under the hood just to make sure they read the same and they do.
I had to build a spacer behind the gauges so the battery wouldn't hit them. I wanted to have a piece of aluminum milled out to fit but used this...a piece of Hardi trim I had laying around.
DSCN1047.jpg
Here is what was needed to move the temperature sending unit.
DSCN1065.jpg
Here it is installed. I had to extend the bypass hose a little. It will raise the top hose a little but I have had no problems so far with this setup.
DSCN1068.jpg DSCN1102.jpg