Apparently our 2004 F550, which was started blowing out huge amounts of white smoke has a blown head gasket. Mechanic says it's going to cost $4,900 to repair. Says he has to remove the cab from the chassis to do the repairs, which include the EGR something or other, Oil Cooler, and some other things that apparently become damged/contaminated when a head gasket goes.

Does this sound even remotely right?