Would a locking differental option be the same as a posi. in 85 c10?

[72farmer]

I just got a 85 Silverado and I was looking at the sticker in the glove box.It has a locking diff. listed on it.So I want to check it out immediately.I tried it in my gravel driveway and it left 2 marks.I then try it on the payment and it only spun one side.As we know in 28 years a lot of things get changed on these trucks.It also had a auto 4 speed trans. on option sheet.What ratio would the rearend be if it is original?