there is plenty of meat to recess the allen key and then punch in the temp sensor while still having room to grab the sensor with a wrench and tighten. if you look at my pics, thats how mine is done.
Judging by looking your hex is a 1/2 wrench though to tighten yes? Mine took a 9/16. I was going to have a machinist from work do it and even after me showing him your photos he agreed that it would take to muchaterial off of my plug.