[Mr70]

That was true to a point.
For 1970 model production,Chevrolet used a more dureable BB valve spring that avoided dropped valves @ higher RPM.
During 1968-9,they started to see an increase in BB warranty claims filed do to unreliable valve springs,so they used the stronger #3970627 to replace the weaker #3859911 spring.
L-88's were exclusive to the #3916164 spring.