The 61 I looked at did not have any numbers cast into it. I've asked for easy ways to tell the difference b/t a 60 and 61 and the only solid answer I have is to get the BOM number off the rear you're looking at and go to Dana's website and decode it. It's quick and easy to decode here... http://www2.dana.com/expertforms/deabill.aspx
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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