Yikes! Prayers sent.
With that said, you can get this truck back together.
My advice to is to attach as many of your replacement parts with small self-tapping screws as possible before welding anything in place.
You will find that as you go along, you will need to move things around. Removing self tapping-screws is much easier than cutting welds.
One other thing to consider is to, "start with a door and build the truck around it." That approach will save you many headaches later.
