looks like some good replies above..
don't know much about V6, mine are all V8..
if it helps, dana tags look like these, good luck!
'71 K20 burb D44 4.09 front [4.10 rear]
'72 K1500 burb D44 3.07 front [3.08 rear]
[moron that removed it left in glove box]
but the chrome cover looks ok tagless
'66 GMC truck D60 4.10 rear