Sorry to say this nico, but your truck is completely a lost cause. An absolute total basket case. Nothing you can do will fix it. You might as well just give it to me and I will drive the snot out of it just like it is.
Seriously, that is a beautiful truck. A stock 350 would just not do it justice. I think a milder cam would be the way I would go too if I just wanted to tame it down a bit. Good luck with whatever you decide.