I found a 12 bolt with the following info: Please verify if my research is correct.

Housing - 3969278NF, GM53
Casting - CON8, B261, 12345, 07890 ?
Stamped on Axle Tube - CHC 082 2E

If I understand what I have read?

70-72 Chevelle
2.73 Gears, August 22, Eaton Posi

I have counted the teeth, and checked the carrier casting and they are 41/15, and carrier is 32088.

My question, if I want to change gears to 3.73 or 3.55, I would need to switch to a Series 3 Carrier, any other changes that would be needed?

Can we tell if this is a 30 spline axle from the info above?

Thank you in advance for your help.

Yep,you got it right.
BTW ,it's a 71 and the carrier is a 2.73:1 down (2 series).
You'll need the 30140 carrier (3 series) to go to 3.08 to 3.73.
Here's a parts list for future reference - http://www.jdrace.com/Rear_ID/12bCHEVY.htm
And yes ,it has 30 spline axles.

Thank you,

So to verify, If I want to got to 3.xx gears, and I purchase a Series 3 posi carrier and gears, I do not need to mess with any spacers, etc.?

Nope ,no spacers with the correct carrier.

Great! Thanks again.