You should be able to do the high idle mod that idles the truck up for PTO use. I did it on my F250 back in 06 when I got it. I don't know if the F550 was any different. It is just a matter of connecting a couple of wires to a switch. I used one of my upfitter switches. Unfortunately it was so long ago i cannot remember which wires are which, but the truck should already be wired for it.
A bigger alternator is a got change even without the pump. I have a 200 amp Quickstart large frame alternator. The older style large frame alternators will bolt on without any changes to the truck.
2006 F250 Lariat Supercrew, ESOF 4x4, 18" tires, FX 4, HD Alt., block heater, Integrated Trailer Brake Controller, Upfitters, power rear window, cab lights - delivered 10/25/05
Ford Remote Start; High idle mod; Timbren load levelers, Scangauge II, Blue Spring upgrade, Quick Start 200 amp large frame alternator replacement, 2 batteries; GPCM replace October 2011; 2 EGR valves; EGR Cooler replaced 12/30/11; Performance Machine & Mfg. coolant filter added 1/2/12; Rotella T6 5W40 oil; turned rotors and replaced brake pads for 1st time 1/7/12 101K miles; GPCM, both subharnesses and all 8 glowplugs replaced 1/5/13 at 118,000 miles; 2 Ford batteries replaced under battery warranty.