I bought a posi unit about 20 years ago for a 8.5 10 bolt and im just getting around to putting it to use in my sons car. the only casting numbers on it are 752. I would like to know how i can identify if this is a 2 or 3 series carrier. The casting numbers for a corprorate 10 bolt posi unit that i have seen on other forums is nowhere to be found. Help?

2 series has the casting number 410409 and the 3 series is number 410408 for 28 spline rears in 2 gens.

Look on the front side of the passenger tube, about 3 inches or so from the end of the pumpkin section. Take a file, wire brush and sand paper, you will find a series of letter and numbers. Then check here for Camaro casting numbers http://www.nastyz28.com/index.php?page=camarorearaxle . :)

Do you just have the case less the axle housing or the complete housing?

You need to be more specific as to where you found these casting numbers.

The casting numbers are actually 725. These numbers are cast into the ring gear flange.There are no other numbers present. This unit is not installed in a rearend it is just the posi unit itself. The numbers that normally recognize a 2 or 3 series carrier are not present. If anyone knows the flange offset difference between a 2 or 3 series carrier i could identify it that way.Thanks in advance for your help.

Here is some discussion of the GM 8.5" posi units, including pictures.
http://www.nastyz28.com/forum/showthread.php?t=59782&highlight=410409+410408
Does yours look like this?

My posi unit is exactly like this with one exception. The casting numbers that identify it are not there.