Builder,
I have installed on-board air on every F350 that I have had. It is real simple and easy to do, and relatively inexpensive. The first two were just the air compressor and tank. On the last two, I had air springs installed and just tied into the system.
Go to AWDirect and order the air compressor, or firestone and order direct. Do not get a cheap air compressor, nor a used or one from a junk yard - unless you can clearly ID a model number and parts supplier. On my earlier 'projects'; I had to replace the motor or something on the compressors often. (about $200)
THen go to a junk yard and get one of the air tanks off an old truck. A 2.5 or 5 gal tank is fine. If all you are going to do is run a line for pumping up tires or blowing stuff off, one or two ports is fine. I ran air horns, air bags, and a line for pumping up tires. (about $5.00)
Go to any truck parts supplier and get the straps to hang the tank on the chassis of your F550. You will have to fabricate some brackets out of angle iron or something. This does not have to be a heavy piece of iron. I got what I needed from Home Depot.
You can get everything you need from AWDirect for about $600.
search air compressor
You can mount these on the chassis right under the passenger door or the bed.
If your F550 has the upfitter switches, you can tie into one of these to turn the compressor on and off. One of the advantages of ordering the kit, is will the pressure switch that will shut off the compressor and 100 psi and restart at 80 psi (I think).
Here is another site to get the parts that you need.
Hadley
I have done this a couple of times, and I will be doing the same when I pick up my F450 in May. So, if you have any questions, just drop me a line.
Hawk