[CPNE]

I6 ps is a different animal than the small block version as there are a few different configurations. You need to make sure that the pump/pulley combo you get matches so the belts will align correctly. I can tell you that if you get Teeitup's pump and brackets, it will line up with your crank and alt pulleys as they currently exist. If you buy another I6, you'll need to swap them over. Do not get anything from a 292, they are different than the 250.

As for the PS box get one complete with the pitman arm. It'll bolt right in and mate up to your steering shaft and drag link. It's not rocket science, heck I've done it. You have a 68 so the frame is PS "ready".

As for the other parts I'd assume from the condition of your truck the FE suspension/steering components are in good shape. If it were mine, I'd toss in the PS then go from there. If you start tearing into the whole thing at once, you may find yourself more confused. If you do have to do ball joints, tie rods, etc, an alighment is mandatory. It is not needed for a simple PS swap.

FYI, here is another pic of a 250 PS setup in my son's 68 burb. Note it uses a single belt. This is why I say make sure whatever you get comes complete with brackets and pulleys, otherwise things may not line up as expected. Again, teeitup's will work with your current pulleys.