From what i hear eaton posi units are the best. I also hear that GM used to use thoughs. I have a 1970 chevelle and i know of a brand new unit which is GM which is bing sold at a classic warehouse for $1500. How do i identify if this gm 3.73 posi unit is indeed an eaton?
i want to do it right the first time around so i came here for some help. thanks in advanced.

I am almost 100% sure that Eaton is all G.M. used for posi units. Will the back cover be off of it so you can check it out?

yes i will be able to take the cover off

Not sure if you're only talking about in Chevelles or not but GM also used and still uses Torsen posi units as well. 7.5" for a Torsen and 8.5" for the Eaton.

GM used Auburn units it later years also, before the Torsen.

Did GM use good Eaton posis at all? Or just the gov-lock? If it's a gov lock and looks like this:
http://i8.ebayimg.com/02/i/02/ee/42/0a_1_b.JPG

GET RID OF IT BEFORE IT BLOWS UP!

Gov Lock = AKA: Grenade Posi

GM used to use Eatons like the ones you can buy I'm pretty sure, the ones with the 4 yellow springs ect.

$1500.00? Is it Gold Plated? Shouldn't be more than $450.00. Check out Summit or Jeg's. You have an Eaton if it is original. Eatons were used (and still are) until the 80's in performance cars, then the 3rd Gen Camaro had the Gov-lock, Auburn Cone-Type, and the Torsen-Style in the SS Camaro.