For 800 bucks I wouldn't complain. Take a hammer to the frame, clean it all out (this is key to preventing future rot), and weld it up. It will be good to go for a long time. Also oil spray inside the frame.
As for the shaking, make sure your steering is in good shape, and check the tension rod bushing cups, they tend to get pretty messed up. Also if it was driven carelessly or wheeled (doesn't look dirty under there though), various front end parts could need to be replaced. Generally working on these trucks is pretty easy unless you've got big hands like me!
I believe those are alignment shims, though I am not too sure.
For 4H you just pull it, it could be stiff from not being used, you can go underneath the truck and spray the linkages with pb blaster and that should make it nice and smooth.
On the plus side, that center link looks new.