The hard lines are rusting? My lines in front are still original, but I've had a rear line rust out twice, near the gas tank filler. Typically you by lengths of straight line (or a roll), and bend them yourself. You can get prebent lines made of stainless steel, but that's a lot more expensive.
I'd recommend getting the copper alloy (NiCop/CuNiFe) brake line and bending it. It's more expensive than regular line, but bends easily, and won't rust. They sell a coated steel line that's not supposed to rust, but it didn't last for me.
The line I replaced was a pretty simple run of straight line, so it was no big deal. If you don't want to mess with a more complicated job, I'm sure a shop would use the copper alloy line if you asked them.
A word of caution, this is a copper alloy that's specifically made for brakes... it's not the same stuff you would find in the plumbing department of Lowes. The stuff for plumbing would work harden and crack, and is not safe for automotive use.
You generally don't have to replace lower control arms. You can replace the ball joints and bushings. Bushings are more of a pain... I've tried on upper control arms and failed. I don't have the tools to do it. I've never tried the lowers. Generally bushings last a long time, so you may not even need them. Mine are original, and look a little old/worn, but I'm pushing 300K miles.
The forged arms you're referring to are from the GMT-800 platform, not the GMT-400. There are people that swap suspension parts from newer trucks, but that's typically for larger/better brakes, not for maintenance purposes... it wouln't be a direct fit, at least not without changing a bunch of other stuff. The lower forged arms from a GMT-400 8-lug truck would swap in, but you're looking at a used part again, and I'm unsure if any other changes need to be made.
