I have the fastcoolers already installed and I have a transmission temperature gauge that was a gift some time ago waiting for installation. Someday I'll get around to it. [Of course, with 5 aftermarket gauges now I'm out of space... will have to decide on a new gauge pod].
I don't tow, so the gauge will be purely for my amusement. I would suggest if you do plan to install it in the factory PTO plates that you have a bung brazed into the plate instead of trying to thread one in. Nick's right - it's probably thick enough, but why take a chance?
-Ryan