"C4" suspension code on my fender tag

Jim Lusk said
No C-4 on my '68 GTS convertible. All 340 cars had the heavy duty suspension so that may have been plant specific for some codes. I do have "624" on the broadcast sheet, however.

My broadcast sheet was missing. All I have is the VIN and the fender tag. Car was built in LA Plant 9/13/67.