What is the difference between Remington model 742 and model740 in 3006?

The Remington model 740 was the first semi-auto rifle chambered in 30-06,and was made from 1955-1959.The Remington model 742 was the next design and made from 1960-1980.I believe that the difference might be the gas piston,and the way the bolt locked up in the chamber(more bolt lugs).