As 3B stated Chevrolet never made a power steering box for the TF trucks, the best you could get was a power assist cylinder setup, which Chevrolet called power steering.
The CCP Series 500 power steering box is 1/2 & 3/4 ton rated only, they don't make anything for the big trucks.
Might be easier to find a modern school bus or truck setup to swap over...
Do you still have to build this as a Right Hand Drive truck?
Mike B
