The ls1 comes with a two wire temperature sensor. One for signal and the other, I don't know. The LS1 Swap Manual I have has an aftermarket (GM Part) temp sensor that has 3 wires on it. One of those wires are for the guage. I installed my temp sensor and the gauge and sensor works. I did pull off the needle and reposition it to make it read 176 at normal operating temperature. It reads acurately up to 210, then kind of gets slow. I didn't want to test it after 210 either.
So, for those of you doing this it works and I don't think there is any other way. Unless you want to tap the head or use the other head. This way looks good and stock.
Hope this helps someone out someday.
later,
allen