From my experience, install the sending unit while the tank is out. But if you don't, no big deal. Its not hard to install after the tank is in. Install the filler neck in the truck. Install the rubber filer neck grommet into the tank. Lubricate the filler neck grommet with a light sheen of...
Once the steering column is coupled to the steering box, there is no play that I notice. If tires are unbalanced etc. then you feel it in the wheel. I would think the bearing guarantees the steering column shaft is centered. Yes, it really looks nice and finished.
I don't think its difficult to find an 72-74 ignition switch. I had bought mine years ago from Ebay but Classic Industries and Year One probably sell them.
If you have the tools, you should take the steering column apart to see whats going on. Like halifaxhop states you may need to replace the ignition switch. So either way the column will need to be taken apart.
Let us know what you find.
I think its a good thing that it is only a /6 because the price would start much higher than someone may want to pay. Look up the cost of body panels etc. that you know you need and base your offer off of that.