I replaced my front springs last year. Mine were in a negative arch. Bought the springs from SD Truck Springs online. Should be around $450 each....and there is a difference between left and right springs, so make sure you order the correct ones for your rig. The kicker is....I had to pay almost $600 for the new u-bolts and shackle hardware from Ford OEM. SD Truck Springs did NOT have the proper sized bolts/hardware. Apparently, there are no direct replacements in the aftermarket and you don't want to skimp on hardware not knowing what grade hardness they might be. I assumed Grade 8 would be the correct answer, but after investigating, I discovered that not all bolts are made the same, even though they are stamped with a particular grade. AND....you may not want a fully hardened bolt that might break instead of give under pressure. Plus, the u-bolts on the F53 are an odd size and even if you try to have the u-bolts custom bent, they don't have the proper dies to make the bend. Better off to just suck it up and buy the OEM hardware.
I had almost decided to try the job myself in the driveway, and after looking at it closer, I made a smarter decision to pay a shop to do it. I didn't have all the proper jack stands and heavy duty air tools or torches to get old, rusted bolts off.
As a side note to that....you can kick the can (replacing the springs) down the road a bit by installing Firestone air-bag helper springs. I did that and got another season out of it. They do help, but in the end the best improvement in my ride/handling was when I replaced the front springs. Of course, now I have both new springs AND air bags on the front. Next project is to install air bags on the rear. Of course, I'll probably end up having to replace the rear springs as well......