I'm confused, are those shackles for the cab only? how could that affect the level of the box? Every truck I have been under, the box is bolted directly to frame members or sleepers clamped to frame members.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy