My 86 has a posi rear from the dash list and from pulling the cover however on my 67 elc , it has large springs while the K10 has 4 posts that almost remind me of minarets with a piece at the ends that goes up and down is this posi or limited slip never seen this type before but I believe its stock anybody have an idea thanks

posi is just another name for limited slip
and it does sound like a limited slip
is there a tag on the diff saying limited slip

The G80 truck option is Eaton Gov Loc. Here is a link on their description. It is not the same as the car posi units as it locks the axles.
http://automotive.eaton.com/product/traction_stability/lockingdiff.html

Edit: The GM service documentation says not to use posi additive with the standard fluid as it can cause extra slippage slowing down the locking function.

Rene
66_Malibu

well thanks a lot for the quick reply however I still have another question I put posi lube in the rear and eaton says its not needed have I screwed the pooch or not ?

I am sure a lot of people do add the additive. There was an old GM service bulletin about the friction reducing additive causing some customer complaints of slower engagement because friction is needed for lock up and the extra slippage could possibly contribute to unnessary wear.
Unless you plow snow or do off-roading I would think it wouldn't be used enough to matter.

Rene