In some resoects, what GM has used for a good while might be considered to be a version of the "locker". Except that they use a governor weight to determine when to lock, rather than something else.
From their product comparison videos, they'll have several competitors' vehicles traverse a concrete "ditch", where one wheel becomes "in free air". In the others, the pickups become immobile when that happens. On the Chevy, as the one free wheel slowly spins, enough to engage the governor, as the "locking" happens, the whole truck seems to shake, and BOTH wheels turn to get it our of the situation.
Before that, they'd put their pickups (towing a then-normal-sized ski boat) up an incline. No big deal? Except that the rh wheel is on a slippery, soapy surface. THe competitors' only get about 1/2 way up before they can't go any farther, as the Chevy continues to the top. These videos might be on YouTube now?
In some respects, these always seemed a bit curious to me, considering that the "limited slip" was only supposed to be about 75% "locking", all along, so might this be a more accurate description of how inadequate the clutches in them might be? Especially the cone-style? Rather than an endorsement of the particular brand of light-duty pickup truck?
I believe that in the later '60s, what was in the 3/4 ton pickups was the "locker:" style rather than the limited slip style?
When the Torsen came out, it was supposed to be "the best" of the breed, but the OEMs didn't really notice, as I recall, continuing on with what they already had. BEFORE the cone clutch models, all clutch plates were flat and had 4 stiff springs keeping everything "locked" until side-to-side wheel speed needed for them to be "unlocked" (as in going around a corner in town). When they didn't unlock easily, the lh side would pop and that could be felt. We have a '69 Chevy C-10 with a factory PTrac, which did that, even with new grease and plenty of additive. Just the nature of the beast? But one that could be fun with the old narrow-tread tires on wet pavement! Even used to advantage, sometimes. But it let us drive into sandy fields which might "stick" a normal pickup. BTAIM
Enjoy!
CBODY67