From what the tech from Zukkiworld said I can use the entire front diff from a 5 speed GV (which is steel) & will bolt right in.
Yes, I've been told that, I've also been told that the ARB air locker can be bolted directly into the rear axle of my second gen.
Here's what I'm going to tell you - I drive a 5 speed GV, and it doesn't have a steel front diff. Some folk will tell you that it has to be a V6 GV with a 5 speed (my daily drive has the 2.0 four cylinder), and to them I say, there is a V6 GV with a 5 speed parked in my mechanic's back yard, and that also does not have a steel front diff - if you're going to pick up the front diff in person, I suggest you walk with a magnet and make sure it sticks
Moving on to the different actuation - the GV front diff has a pneumatic front freewheel mechanism that is internal to the differential, which the Sidekick doesn't have. To make this work as designed you need the air pump that sits behind the front bumper, this is around USD$400 if new, and the 4WD controller module, some GVs have this module as a separate box (mine does), some have it integrated into the ECM/PCM - just my opinion, but $100, sounds a little unrealistic.
This front freewheel mechanism is a known weak spot in the second gens and second gen owners weld them together or replace the entire differential with one from a first gen - this should not be a problem if you're installing a locker which replaces the differential case.
Aftermarket lockers - as I mentioned earlier, as far as I'm aware, there are NO lockers that fit the front of a second gen, or the rear for that matter.
What you're going to need to do is find a steel front axle assembly, and then mix & match - bolt the ring & pinion from the steel assembly onto your first gen differential carrier (if you're using a lunch box locker) or install the complete locker with the ring & pinion into the steel third member and fit everything up.
Now - let's go to the rear - because I'm sure you know the rear axle gears need to match the front axle gears.
As I mentioned earlier, I was told that the ARB air locker can be bolted directly into the rear axle of my second gen - that did NOT match my experience.
Sitting on my garage floor is the rear differential out of a second gen, a twin to the one I daily drive, the remainder of the axle is at the back of the house. I bought both front & rear axles out of this GV with the plan being to get them setup and then take a weekend and put them under my daily driver. The internal diameter of my "spare" ring gear measures in at 108mm, the external diameter of the ARB RD209 is 118mm, my ring gear is also about 5mm too thick.
Officially the fix for that is to swap, yes, you guessed it, the third member from a first gen into the second gen - this by the way, is not an option going the other way, the upper wishbone on the first gen suspension mounts to the third member, the second gen third member doesn't have the mount, so, again, to get the 4.3 gears in your rear end, you'll need to pull them out of the second gen third and transfer them to yours, and whilst I think that it can be done, I'm not 100% certain - that ring gear thickness could be a stumbling block - in theory, a spacer could be machined to move the ring gear closer to the pinion, but I would suggest you consult a differential specialist on the possibility of bolts shearing, being too short, etc.
In a nutshell, you are venturing into uncharted territory, expect there to be challenges.
will surely be cheaper/simpler than any swap
