I used to make these white box trucks. I don't mean ones like it- I mean, the company I used to work for made this one. The company is called Supreme Corporation. I've literally put together thousands of them. I used to be the lead man over the main assembly line in the Georgia plant. I've done about every job there is to do there (this was before I joined the military). Put together the floors, the rear doors, the lining on the inside, even painted them and held down the Quality Control slot for a while.
The width of this truck's door will be 85 and one quarter inches. The height will be either 77, 83 or 89 inches (note, these are inside door opening measurements- not outside body measurements). The Astro is 75 inches high and 77.5 inches wide.
On a side note, it is possible for the shooter to be on the inside of the truck with the door in the down position and locked and make his shot without his partner (?) getting out to unlock the door. The top panel for this type of roll up door (most likely a Todco) is adjustable. You can take the top rollers out from inside with a 9/16 wrench and the top door panel will fold down towards the inside. Theoretically, he could take his shot and quickly fold the panel up again and even if somebody looked in his direction, all they'd see would be white truck with the door shut and latched. His partner could crank up and drive away and nobody would have ever seen anybody with a gun. Nobody even need get out of the truck. His partner could find a suitable spot, park the truck with the rear pointing the right direction. They could communicate with cell phones. The driver tells him when it's all clear. The shooter folds down the door panel, picks out a target, makes the shot, the driver cranks up and they're off.