At least in my 98 Limited, the ARC controls the ride height. If you disable the system and just install standard shocks, loading a lot of stuff in the back will result in a weird posture and perhaps even scraping the curb with the rear of the truck. Guess some people handle this by installing stiffer springs or using a lift kit.
Unfortunately, the original Ford air shocks are no longer available. Motorcraft now sells the pricey Monroe-made replacement that someone already mentioned here. Rock has those for about $200 apiece. I recently installed those in the front and must advise that while they seem to work just as well, they are a lot more pain in the neck to install. First, the outside diameter is significantly larger, so it takes maneuvering the control arm to that one 'magic' spot that even allows you to get it in. More importantly, they have no flat surfaces to hold against rotation when you are torquing the nut. Their construction does not match the original Ford rubber 'cushions' and you have to use the Monroe hardware, which is much smaller in diameter and clearly inferior in quality. And finally, unlike the originals, they don't have the electrical control for stiffening the ride in off-road mode.