Well, I bought a electric temp gauge from Amazon for $12. Pulled the old sensor and tried that with the gauge and it didn't work. The new sensor worked fine. I also checked and had some adapters that were the British BSP 1/8" thread that some people on here have said was the type of the old sensor, but I checked and checked again and my thermostat housing is the standard 1/8" NPT pipe thread. None of the 1/8" BSP threaded fittings would fit in the housing. So it was a direct fit because the gauge came with a 1/8" sending unit. No drilling and tapping required.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1