[Berg]

Someone has put a pickup bed tailgate onto your Blazer. There isn't too much missing if you find someone parting out a Blazer. You are missing:
Tailgate and window assembly
Tailgate stop cables and bolts,washers (these mount to the side with bolts, you can see where the bolts used to go
Tailgate torsion rods (these slide into holes in the bottom of the tailgate and bolt into the sides with retaining brackets. Use stamped metal retainers and bottoms have plastic/teflon isolaters.
Tailgate hinges. They bolt through the tail pan from the bottom side of the truck into little pockets. The tailgate has corresponding pockets for the hinges also.
Don't forget you need to take off the trunions and tailgate latches for the pickup parts since the blazer latches use different pieces. Don't forget the shims for the latches to properly engage too!
I hope it works out for you, I tried to copy a diagram of the tailgate and all related hardware. I hope it helps.