Can be fitted front or rear but please note fronts and rears are different due to the difference in preload.

When both wheels have equal traction there is minimum torque bias, equal torque will be transmitted to each wheel. In this state the diff will be unnoticed by the driver even when used in the front axle. If one wheel begins to loose traction the gears work against each other and the support case. The effect of this "inefficient" gearing is to multiply the torque on the wheel with the least grip i.e the one that is trying to spin by up to a factor of up to three to enable the wheel with grip to drive. A simple test is to have someone hold one wheel and note the effort to rotate the opposite wheel,it will take approx three times the effort. The advantages of this type of diff centre are that it is very soft in operation and virtually undetectable when driving on the road, disadvantages are, because of the way they work you need preload on the spinning wheel in order for the diff centre to bind up and transfer torque to the other wheel, in some situations such as a severe axle twister when there is no preload the Truetrac will do very little. It can be fooled into working by left foot application of the brakes to pre load the spinning wheel but really in this situation a locker is required.

More info can be found here,

Remove the diff from the axle case, you will notice the replacement diff centre is the same fitting as the old two pinion centre. Match mark the pinion bearing caps and remove the old centre from the diff housing, remove the crown wheel from the old centre and fit to the new centre using locktight between the mating faces and on the crown wheel bolts. Note the faces must be cleaned with a solvent cleaner to remove all traces of oil to allow the locktight to work properly. Fit the new bearings to the new centre and offer the assembly to the diff case, there is no need to remove or adjust the pinion but, if thought necessary, it could be checked at this time. With the new centre in the diff case and the correct bearing caps fitted, adjust the side adjuster nuts to give the correct backlash (.004in to .007in) and bearing preload (as per workshop manual). Finally tighten down the bearing caps to 60lb ft and re check the backlash, tag the side adjusters. Re-assemble in the axle case and carry out the pre run test as recommended in the Tractech instructions for that particular unit, be sure to re-fill with the correct oil i.e. normal diff oil.