Electrical Aftermarket and stock temperature gauges working in harmony?

There are two 3/8npt ports at the rear of the lower intake. The pass side one is usually occupied by the return line for the EGR coolant line. The drivers side is usually just plugged.

relocate the stock temp sensor to the rear of the intake manifold in that 3/8npt port and put your aftermarket temp sender in the oem location.

the rear spot reads a tiny bit cooler than the oem location, but it will rise and fall like original so it’s a good backup guage once you understand how it reads compared to the aftermarket one

This is how I ran my setup for many many years