The pump is probably fine. I would not suggest a used steering box. It was rare to have a 4 or 6 cylinder to leak, but just about all the V8s eventually leaked and needed resealing. The cause is the heat generated from the exhaust manifold. The manifold is rigt next to the box which wipes out the seals. If you get a used box from the breaker yard,chances are it will also leak.

Good luck,
Peter

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