If that is the reason you went with the Ford van, this is my recommendation:
DO NOT EVEN THINK OF GETTING A PH TOP!!!
Here's why I say that:
My van has factory rear air. Here is a picture of the original installation:
I currently live in AZ. My kids almost died (almost not kidding) riding in the van in the summer.
Here are some pictures of the improvement during install:
It is a plenum that runs nearly the length of the van on the driver's side and has six vents.
Sorry I haven't taken a picture of the finished product yet. It is significantly better than the original solution. However, in the heat of the summer in AZ it is no kidding boarder-line dangerous to take my kids anywhere in the van if it doesn't get about an hour of the a/c running first.
So, if that volume of a/c is a requirement where you live, I suggest that cutting a big hole in the top of your van will be the single biggest mistake you could make for the daily usability of your van.