Hi - I had few emails about the Tufport roof so here is some info and also some pictures.
The interior height, from floor to ceiling, inside the barn doors, behind front seats is 72 1/2", at the back of the van about halfway back it increases to 75 1/2". Now my carpeted floor is probably 1/2 thick so for the actual height from bare floor is about 6'1" in front, and 6'4" in the back.
I got it from Tufport in Vancouver BC, cost was about $4400 Canadian installed - they installed it in a day.
They also installed a high quality light, and a roof vent. In hindsight I wish I had got the electric fan roof vent, I just got the vent with a screen and no fan. I did not get any side windows as the van has about 12 windows already !!
I was very impressed with Tufport, they made the whole process easy. They had the exact mold for the E350 extended van so this was an easy choice for me. They do a lot of commercial vehicle work so I knew the quality would be really good.
One other point - you can choose how far back you want the roof to be cut out, I chose the whole roof, but some people might like to keep the back 3 feet as roof, for a solid area for a shelf or cabinets or for 1/2 of a bed. I ended up having to build a shelf anyway so I may have been better leaving some roof !!