Try the Chevelle suppliers. Ground-Up Restoration is where I bought a set of four last Fall for my car. "Mechanic" at the spring shop knew how to use one tool & one tool only.Impact wrench set at about 1000 lbs!! Twisted two off & installed short bolts & hex. nuts. Found out when the car was later off the ground for oil.
GM part number 339715 is the newer style replacement. I like them as they are one piece instead of the captured nut design so less chance of them coming apart. Also incorrect for the purists. later Tim