What is this rear end code for 1975

[stano]

What is this rear end code for 1975? Is there a page for rear end codes?

RFHG 3422

The casting number is # 3977323
The casting date is I 6 4
It rolls over as a 3.73

But I have not opened it up to see if it is a open or locking. I thought the code would tell me?

thank you
stano
87 K5

 

[goldwing2000]

I have a link to RPO codes but not axle stampings.

http://www.drivetrain.com/GMtrkratio_posidata.html

Last one I had to check, I went to an old GMC dealer and they were able to look it up for me. That was almost 10 years ago, though.

 

[theperfectgarage]

My decoder ring ( which is not always correct ) said it's a 3.73,8.5in.ring gear, 10 in. brakes non locking from a 90 to 91 K series 1/2 ton.