Yeah, it looks like the F550 cab and chassis models are available w/ a 200.8 wb (regular cab) or a 200.2 wb (crew cab), among other wheelbase lengths..
These are 2015 numbers, but I would assume previous years would be the same..
Wheelbase
Regular Cab: 140.8" (60" CA); 164.8" (84" CA); 188.8"(108" CA); 200.8" (120" CA)
SuperCab: 161.8" (60" CA); 185.8"(84" CA)
Crew Cab: 176.2" (60" CA); 200.2" (84" CA)