Water temp guage
http://www.autometer.com/accessories...harnesses.html
They also have an install kit for LS engines, with the required fittings. The link below even comes with the short temp sensor ($35).
http://www.autometer.com/ls-install-kit.html
In the long run it is better to spend a few bucks right now to get the proper part. Once you drill, you're stuck with your new size hole.





