The steering box looks to be through mounted to the frame but I'm not sure exactly how - maybe an adapter plate? I'm 90% sure the slop has to do with the blown rod ends - the pitman arm rotates a few degrees before it eats up the slop in the rod end, leading to oversteer.
As for the rust, I'm guessing there's more there than I can see, but I'm ready to accept that and if it comes to replacing panels over time... well, I better start saving my lunch money now!
Good point on the rear drive shaft, didn't even notice that at first!
Price wise - he's asking $5500. On the higher end of what I'd pay for this truck, but the Missus thinks it's a fair price to get me a project and keep me occupied. I guess I don't have enough projects as is!
-Kevin