who can tell me the difference between springs SB abd BB for a chevelle 66? I need the springs but in the Ground Up restoration manual there are the two types.

The differences will be in the wire diameter and ultimetly in the spring rate. Different options added weight or subtracted weight from the front and rear of the vehicle. The big block was a susbstanial increase in weight over the big block so they usually got different springs to compensate for the heavier weight. Air conditioning cars also got different springs becuase of the weight that an AC system adds.