K10 Blazer HELP

[83Frankenstein_GM]

I bought a 1983 GMC Fullsize Jimmy. I knew it was a rust bucket when I bought it, I have known the guy I got it from since I was in diapers and he had it since new. It has a snow plow on it and basically he sold me the plow and gave me the truck. Well upon lowering the tailgate recently it fell off in my hands and the floor is very rotten. I bought a cab from an 86 Chevy pickup. and I want to build a flatbed. Any advice on pulling the jimmy body off, putting on the pick up cab and best way to build a wooden flatbed. I'm not a mechanic or a body man, my father has a background in mechanics so he is going to help me but we still would like some advice.