Thought I would add an update to this. The dual-contact sender didnt work out, so I ended up going the "T-fitting in hose to water heater" route.
Everything seems to work, but the gauge never seems to exceed ~102F no mater how long I run the engine for.
As it turns out, I didnt have a 2GMF, but rather a 2GM with a fresh water conversion.
From what I can tell, the water going to the water heater is always a mix of what was allowed through the engine by the thermostat and the water that was routed around the engine, which may explain the low temperature.
I'm still not totally sure I can trust the measurements I'm getting, but I've not overheated yet, so we shall see.
-dan
