So far all my drive train on my 67 326 ho 4 spd is original and I started looking at my rearend tonight. I didn't research much about it and the first thing I see are the loops cast above to pinion. I thought this isn't even a bird rearend but they did a nice job adding the dual traction bar brackets. I fired up the wire brush and couldn't find any letters stamped on the drivers side tube. So I took a few pics and researched the casting numbers and I believe I have a nodular unit cast the 12th day of 67 which lines up within a month of everything else. I think I'm on to something.