Hi Arizona,
Start with a REZ Engineering Adapter plate. DO NOT attempt to bolt the power steering box directly to the frame for two reasons.
The first is that the lower bolt will align below the frame rail leaving only three mounting points. The second is that with power steering, these frames are notorious for stress cracking. The REZ adapter includes a backing plate that adds strength to the frame significantly reducing the chance of cracking. The adapter will align the box perfectly to the column as well.
On the column side, if you keep the original "javalin" (as in spear) column, you will need to cut to shorten it, and replace the rag joint with one compatable with the box.
When I did mine, I installed a rebuilt tilt column and replaced the rag joint with a Borgesen universal joint. I then used a new Double D shaft cut to fit, and installed a Borgensen steering dampner at the end of the column.
For a steering box, use a 1967-72 800ps box. I used one that was "performance tuned" to 2 1/2 lock-to-lock turn.
Aside from disc brakes, the best improvement you can make to these trucks !