I have a 3.23 Dana 60 in my '65 Coronet with a Doug Nash 5 speed. I think it is just about the perfect combo. The Doug Nash has a steep first gear (3.27) and then fifth gear is 1:1. It takes some work to get the combination all dialed in since everything really depends on the camshaft and the torque curve. I'm not a fan of the double overdrive transmissions since 6th gear is almost useless. I had 3.54 gears in my car for a long time but it was just a little too deep for daily driving. Cass developed the 3.23 gears for the Dana 60 and so I took the opportunity to switch to a new Strange S60.