GM not only used the same Saginaw steering gear box in every car they made from 1965 and up but they sols the steering gear box for use in Fords, and Chrysler Jeeps (the rest of Chrysler's line up used torsion bar suspension which interfered with the standard steering arrangement used by everybody else).
Prior to 1965 the steering, especially the power assist was very different than that used from 1965 and up. Rather than put the power assist hydraulic piston inside the steering gear box like it was done on newer cars; the Chevy engineers used a manual steering gear box, with the gear box controlling the line pressure to a slave hydraulic cylinder, bolted to the frame and tie rod the way it is done on agricultural tractors and large heavy duty trucks. It is simple, and very effective, because if you loose hydraulic pressure you can still steer the car (which is why the Corvette retained this system until the early eighties).
If you have ever tried to steer a power assist gear box with the motor off you know what I am talking about. Which is why Chevy is being sued for the ignition switch problem. Keys fall out turning the switch to off; either locking the steering column, or making the car hard to steer due to no power assist. Then when it finally crashes, the air bags do not deploy because the ignition is off.
Whether a Jeep box will bolt up and clear your custom radiator I do not know. Usually the steering gear box is an upgrade made to a manual steering car without all of the hoses and the added large hydraulic cylinders that is attached to the car on a power assist.