I was going to do this a while back when I had my 85, I still actually have all the wiring and dash for the 87-91 truck. All the research I did on it made me realize it isnt just a direct swap, you will need to go to the junkyard and saw off the mounting tabs off the interior of the cab of an 87-91 truck. Im not saying it can not be done, it can with a little work and patience. All your wiring will need swapped to, and the firewall will need drilled out to fit the new big round fitting that is from the 87-91. Do you have the wiring? If not send me a PM, ill hook you up good.
Everything else IE the door panels and other accessories would probably be a direct swap.