Back of the transfer case behind the parking brake mounting plate. Tight little hole near the top. Just past the big nut on the back of the box.
The small black Y shaped piece in the picture is the mounting plate for a cable. Take it off and use the existing bolt/stud to mount your transducer.
One addition to that. Make sure you have the correct size input. They are 2 different sizes. Inside the hole is a square piece the transducer pin goes into. I have heard of people using a spacer to make the small pin work with the larger input. No experience with that myself.