The system I installed used a probe that pushed through the cooling fins on the radiator. I installed it near the outlet or lower radiator hose. You can buy a t-stat housing that has a threaded hole in it for a temp sensor and some intakes have an extra hole that is pluged with a pipe plug.
If you want to run the fan with the currant engine most parts stores carry an electric fan switch and relay kit for about $20.00. Its like the one I installed and you just push the probe through the fins on the radiator.

I didn't do it, no one saw me do it, you can't prove anything! "Bart Simpson"