on one of the RV forums I follow, they stated that to work on the engine in a F550 you have to take off the cab. are they talking about major engine work like replacing injectors, etc?

 

Almost all repairs can be done cab on, including head gaskets and engine removal, however head removal/studding and anything requiring engine removal is much easier with the cab off and if the proper equipment is available the cabs come off very easily, they are designed that way.