A complete replacement is a HUGE job fraught with the danger of not bracing the cab adequately and tweaking it out of alignment. Is it that bad you need to replace all? If it is have you considered sourcing a decent replacement cab. I have sold/owned lots of these trucks and good cabs are available and a lot less work. I would look at all the options if the floor is that bad how are the cowls and corners they have to be bad too?