[Mr70]

They used different springs,for different weighted cars in general.
Four door,two door,small block,big block,convertible.
GC callout suffix was used on many 1970-72 Chevelles w/various weights,but that particular spring number wasn't.
That's the brief early 1970 Big Block Heavy Duty front spring,that was only used only on the brand new 1970 Chevelle coupe./Convert.& Elcamino when equipped w/either Air Conditioning or a Big Block,or both.
It was soon superceded by spring #3960665,beginning with late 70/early 71 production,and still coded as their GC Heavy Duty ft.spring.