Locks both axle shafts together so they turn at equal speed and power.

gen1 V6 have 8" front axles which are stronger than 7.25" 4cyl. axles (like your 87) they have lockers available.

I locker is FULL time 4wd(if both front and rear are locked). You may have noticed some time in your life than when a tire comes of the ground it spins like crazy and the that does have traction doesn't move. Well, a locker "locks" both axles and the wheels will turn in any situation unlike an "open" diff. You'll want it if you plan to wheel alot <img src="/forums/images/graemlins/kewl.gif" alt="" /> But, this is why you need the 8" diff. Lockers break axles with real big tires ~35"+
You WILL need lockout hubs with a locker or you will have horrible turning radius and tear wear.
some Gen2 rear ends 92-99?00 had optional airlocker which can either be open or locked. Better for the street when open and good for wheelin when locked. Those come on 9" and 9.5" rear ends which you will probably never break.

<img src="/forums/images/graemlins/kewl.gif" alt="" />

Locker to me means switchable, or something that ratchets like a Detroit. IOW, you don't HAVE to have hubs to turn tight, you just disengage it.

Said statement excludes Lincoln lockers of course...

If it were me, and you plan on keeping the 87 and playing with it, I'd grab pretty much the whole front end, and also the brake master cyl and vacuum hose.

OK, thanks for the explanation, it makes some sense to me now.

I like deep snow. I've read on here experiences with front starion LSD setups on snow filled streets and they sound kinda squirrely for that use. I like open diff for 4 wd unplowed steets and the locker when I get burried off road in Sierra snow...