Posi unit measurement, 8.2 or 8.5?

I'm ebaying some stuff for a friend and have a posi unit that he says is out of a late 70's T/A, if I remember correctly, GM switched to a 8.5 in late 60's, right? What do I measure? Overall ring gear diameter, being outermost measurement.

http://buickperformance.com/posi.jpg

Post the casting number...

http://buickperformance.com/posi.jpg

Post the casting number...

Its at home but if memory serves me it was 410409 N

That's a 8.5" 2-series carrier, designed for 2.56 and numerically smaller gears. The 410408 carrier is for the 2.73 and up.

Its at home but if memory serves me it was 410409 N

I'm thinkin that casting # looks more like a 6 or an 8 on the end than a 9.

The picture is from a Buick site from an article called:

How to Find and Remove 8.5" GM Posi Carriers by George Nenadovich

It carries the caption:

The 3 series carrier will have a casting numer of 410408 on the right side (pass. side) with four large "8"s also on the carrier. Please see photo below for the casting number(between the two 8s) and two of the large "8"s .

http://www.buickperformance.com/posi.htm

Mike, do you happen to know if these are 28 or 30 spline, I got it on ebay and some guy is asking, its at home and I'm at work.

Thanks

According to The Z28 guys, the corporate 410408 8.5 posi had 28 axle splines.