We live in a 6'1" International and my hair bushes the roof. I don't find it uncomfortable but space would be nice, so I'm sure you could do it if you had a bus at 6'4". That said, the bus we just bought to convert is 6'4" inside. There are a few out there I've seen at that height and a few taller so if you do a little looking you could probably avoid a raise. Or embrace the fun.
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