In tractor applications, the temperature gauge is mechanical, using a capillary tube. That's the bad news. The good news is that electrical / electronic replacements are generic and plentiful. A standard Stewart-Warner sending unit will probably work with or without some sort of adapter. Is...
Heat dissipation. You might be able to obtain a solid-state replacement that runs cooler or which has a built-in
heat sink that sends the heat out through fins on the front.
There's a special place in hell for people who won't learn the difference between adhesive and bedding compound. In it, they're forced to go about with a 1-gallon can of Dolphinite attached to their backside with 5200.
Time to start making local contacts. Drop in at the friendly folks at your South City West Marine. They'll certainly know "a guy" locally who can fabricate a tiller for you. Failing that, stop by the boat shop up at San Francisco Maritime National Park (say hi to the Thayer for me) during normal...