The 3.55 was the default axle ratio for the L78 cars..at least from all the info I have seen. Yours has the E stamp which stands for Eaton positraction. This was an option on the 12 bolt rears. I believe you could also order the 3.55 ratio with the 396/350 hp L-34 and the 350/300hp small block SS Nova. The 3.55 was the "steepest" rear gear available in the Nova for 1970. Though I am sure there were lots of 4.10's installed prior to delivery.