Rear Axle question

I have a 1979 10th Anniversary with the 403CID and Automatic. My build sheet says I have a 2.73 rear axle. My question is how do I know if I have a 2 or 3 series. From the research I have done it indicates that the 8.5 rear is a 3 series and the 7.5 is a 2 series. Is this correct? Also how can you tell from the outside? I know the clutch type is a 8.5 and the cone type is 7.5.

Thanks in advance for your help.

Jim.
The answer is a 2.73 is a 3 series.
I took the liberty to post your question
over in the 78TA Tech forum..
Jeff (The resident Tech Master on that site)
awswered your question.

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Martin,

Thanks,

Jim

Anytime Jim.......I hope all is well