I have had overdrives for over 50 years...Borg Warner, but the top 2 is about the same split. 3.90 is ideal. I used some 4.11 in my Y-Blocks which gives you a little more power in overdrive, but I don't think GM made a 4.11 open rear. You must remember these old engine are happier at higher rpms than current production engines, even if they don't sound like it.
