ASTM A 300 is titled "Notch Toughness Requirements for Normalized Steel Plates". This material specification provides requirements for impact testing for low temperature service. The Class 1 designation only applies to A 516 steels, all grades, with a minimum impact test temperature of -50 deg F. Minimum impact requirement is 15 ft-lbs.
So, yes, you can use SA 516 Grade 70 material but you need to specify heat treatment and require impact testing for Class 1.