FWIW: I'm the guy pictured above. Having the roof raised (ECCB is right I'm 6'3) is CRITICAL. You'll be uncomfortable walking around your own home for 2 years. For me, that's unacceptable. With the flooring put in, and with insulation below and above, you're going to lose precious inches. I've already hit my head (too many times to count) at exactly where the transition occurs. 2 years is a long time to suffer through hitting your head every time you stand up or walk around.
I have seen plenty of threads documenting roof raises. If you can hire a welder, all you need is basic handyman skills, time, and a few friends. Most of the stuff I'm doing in the bus is stuff I've learned on YouTube. You can do it too.