the trouble with the mechanical sensors, is the huge [comparatively speaking] size of the bulb that must go into the liquid [in this case, oil] being monitored.
in this case, as has been said, welding a bung in the pan or fitting[s] adapted to a cooler is about the only choice[s] available.
electrical gauge 1/8npt sending units allow many choices of places to install them, and today's electrical gauges [quality ones of course] are as accurate as mechanical ones.
i realize we are talking mechanical gauges, but i'm just expressing my life's experience. not looking to pile on anyone, or start an argument, so please don't take offense.
i used to believe in only using mechanical gauges, but in my old years, i have changed my mind. i have a complete set of mechanical gauges [S&W stage 3] for my endless project, bought many, many [and even more many] years ago.
if i were buying something today, i would look to electrical units. however, i have the mechanical ones, so i will be using them. [i will also be looking for a good place to install an oil temperature bung. kinda' ironic, eh ?..... ]