An update of sorts - I found a control unit that should work for what I'm doing.
Power Steering Controller
This unit will take a speed input off a Corvette ABS sensor and will let you control the amount of assist a power steering unit will give. Unless something changes, I'm going with a Corolla EBAS unit that mounts to the firewall and provides assist on the steering column, which will move a manual steering rack. This should be plenty strong enough to turn the front wheels on a slightly heavier vehicle that is not using the front wheels to drive the vehicle along.