Back to the original topic, which is a 68 GT500 C6:
All of these are identified by PGB-W tag code, if it is still happens to be attached to the servo (H servo). The correct main case has different casting characteristics which allow it to fit properly in the F body. An A body, or truck C6 is not the same main case. Those may mount to the chassis, but there are other clearance issues without modifications.