There are two different sizes of glass for these vans.
Yours looks like one of the "newer" style that is held into the frame using glue and uses external and internal trim rings, which is a little bit larger than the gasket-type.
If you can get all that crap out of there and your windshield frame sheet metal isn't rusted all to hell, clean it up with a wire wheel, re-seal all the seams in the bottom corners and replace it with the smaller glass (windshield # 853) and a quality rubber seal.
There are a lot of them them on the market, some good and some garbage. After trying a few, I've found that the only one worth using is two-piece seal made by Precision Premium Automotive, part # WCR-853. The locking key strip that presses into the center is part # WLS-466.