Check out my Feb 7, 2020 post #57 on the "Exasperated KJ owner!....." thread. I posted drawings for modifying the oem thermostat housing to accept normal thermostats. There's lathework and welding involved.
Turbo-diesel-freak's thermostat is the best way to go. If you have one ordered it'll eventually show up. I thought mine wasn't ever going to show but it did.