I agree with Fibonachu. No one welds on a frame just for giggles (and shouldn't weld on it at all unless absolutely necessary).
As far as rust removal, sandblasting is probably the best, followed by epoxy primer. But since you won't be able to reach all the nooks and crannies with a blaster, Some sort of rust converter paint as Ferris suggested would be appropriate. Be careful using acid products, as they need to be completely neutralized before coating.
Post your questions about overload springs over in Driveline. Those type of overloads were used from the factory on bigger stovebolt trucks. No reason you couldn't remove them if you're not planning on carrying a big load in it.
