The problem with using a through bolt and nut to replace the missing weld nuts is that the factory nuts are very heavy duty thick nuts and are used to locate the steering box and take shear loads from the steering forces.
The nuts are typically big square nuts with lots of material on them, but the top of the nut is a cylinder that is a close tolerance fit into the holes in the K member. This restrains the nut from moving sideways. If you put a bolt through the now empty K frame hole, no matter how much you tightened a bolt and nut to clamp the steering box, the K frame hole is much larger than the bolt you would use. Aside from the fact that you now have extra work trying to align the box properly, the operating loads would overcome the clamping friction between the steering gearbox and the K frame. The box would move around and make driving exciting.
Andy is right, it might possibly be fixed, depending upon what other issues there are that can't be seen here. But, unless it is some rare valuable K member (which is unlikely if you got it from a wrecking yard) I would trash it and buy another K member.
Robert