I did this, but I used what was supposed to be an engine temp gauge. The only difference between them is the size of the sender. I already had a drain plug in the back of my transmission pan, so I enlarged that and mounted a fitting in the hole that would accept the sender. Now to drain the oil, I just remove the sender.
There are three ways to measure the transmission temp.
-pan
-oil send
-oil return
The pan is generally considered to be the best all around measurement for safe operating temperature. Anywhere that the sender is dunked in pan oil is fine. The hottest measurement will be the oil send line, as that is oil coming directly out of the torque converter. It will be especially hot if you don't have a lock up converter. That is where most of the heat will come from. However, you can hit 250 degrees on that line without bringing the pan over 160 if you have a good cooler. Generally you just need the pan temperature. B&M recommends putting a line sender on the return line (cool) instead of the send line (hot). Personally, I run one in the pan and one on the send line. I plan to someday buy a seocond sender and put it on the return line so that I can use the same gauge for both, just by flipping a switch. That's part of the beauty of electrical gauges.
Good luck with whatever you decide to do.
<font color=green>"Do not replace belt while engine is running" --Warning on a Kelly Srpingfield package</font color=green>
