There's an ongoing thread about the quality and reliability of this turbo here:
http://www.supramania.com/forums/sho...d.php?t=102040
One thing that is backed by the opinions of some VERY knowledgeable people is that this turbo should absolutely NOT be run with the stock elbow (the 90? bend with the O2 sensor mounted in it that's mounted to the back of the turbo).
You only have 2 sensor locations on the thermostat housing? If so then I presume it's because your car is an '88 or older. The three position thermostat necks was on '89 GTEs and newer if I recall correctly.
Here's what the sensors are and their locations: