Chris,
I think you would have to be very lucky to find a power steering box that mounted close enough to the stock box position to be able to do a unbolt-bolt swap.
I would be concerned that a modern column, especially a tilt setup, would have the durability to turn a manual box and survive for very long. Because they twist a powered box, they are usually pretty skimpy on 'heft' if you get my meaning.
I could be wrong about this though, it's happened before.
Stuart
