I´ve had a bunch of themrostat failures over the years. Some stuck closed, some stuck open and some I messed up with the installation.
Any old thermostat won´t do, the jeep thermo is a low profile thermo, to clear the bend of the elbow. The OEM gasket works best, cut your own as a second best, no gasket and silicon as a third best (being careful not to overdo it and gum up your new thermo). And throw away the universal gasket that comes with some thermostats.
A standard size (hight) thermo can be made to work, but you have to be careful. It will only fit in the elbow one way, without crushing, hard to install, with the hoses still hooked up, hard to feel when it´s wrong. It will crush when the elbow is tightened.
I do have an old truck mud flap, that I put in front of the grill on occasion (for mud not cold). Drilled a couple of small holes in the side of the headlight bezel and use a couple of bunge cords to hold it in place. Havent lost it yet.