Not knowing what your plans are for your project, I just want to say that my '57 2 ton truck loaded with 110 bales of hay probably weighed 11,000 - 12,ooo pounds, the stock brakes have no problem controlling the decent, I rebuilt the entire brake system with cylinder kits and a Hydrovac kit.
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