I agree with the THEMULE69. Even though the factory installed gauge is in the wrong place -- you don't care what the temperature is at the top of the cook chamber, you want to know what it is at grate/meat level - I'd leave it where it is. Additionally, bi-metal gauges (1800"s technology) are very inaccurate. They can be off by 50*. Invest in some type of digital unit -- like Maverick. They're expensive but so is ruining a expensive piece of meat.
I had an extra Tel Tru from a unit I sold and I installed it on the chimney. Don't ask why -- I don't know it just looks trick and is a conversation piece for non smoking friends. At the time I was drilling a hole for my temp probes and the chimney seemed like a good spot. It was an expensive thermometer and I didn't want to store it.