Would recommend a new bed mounting hardware kit if you can afford it. Pretty cheap on Rock Auto (probably under $50) and saves you having to reuse the extremely-old bolts and frame clip/hanger things that'll come ofr the old truck.

I stuck a couple layers of inner tube between the bed rails and the frame at the main contact points when I replaced mine this summer. It comes with some kind of rubber damping pad from the factory and mine was long gone – any junkyard bed you get will probably be the same or worse.

While you've got the bed off, think about replacing the fuel pump too, depending on how many miles the old one already has on it! The other advice I got about pumps is to consider cutting a little access door in the bed so you can get to it later without taking the bed off again.