I guess the answer would be "Check with the maker of the Lockrite."
As I understand it, there are two types of passive locker systems: one that uses the side gears and one that replaces the sidegears with it's own components. Since I don't know which group the LockRite fits into, I can't give you the ultimate answer. However, I would expect that, if you have a rear LockRite and it uses the existing sidegears, then all you have to do is come up with a set of rear 26-spline sidegears to make the differential work. It will bolt into a front carrier as the carrier in the front is same as the rear.
This is
not the case on the Sidekick/Tracker/Vitara, which may be the source of confusion to you. It Internet is sometimes not the best place to get a straight answer.
If the LockRite uses it's own replacement components for the side gears, then a rear LockRite will bolt into a front carrier as long as you use 26-spline shafts.
{edit: sorry I was so long-winded - the posts below are the Reader's Digest version

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Hope this helps!