Can you post a picture of your intake, around the thermostat housing?
I have installed mechanical gauges in 2 intakes before. I know it can be done, even with a factory sender.
The water port runners had a 1/4" wall thickness, and with thread sealant, it will hold, and will not crack. A torque of 18-20 Foot pounds is enough.
They also make thermostat housings that "rotate", (time to improvise) but you may need to get a different upper radiator hose, to make it work without putting a 'kink' in your hose.
In a case like this, you need to be able to 'think outside of the box' to make it work.
Disregard what is the 'given', step back, look, and think 'how can I make this work'.
to Hot-roding 101.