I just recently put an AllPro flat bed kit on mine and I love it. I have an 82 with an 84 cab on it and it seems to work pretty good. Things you should know, AllPro kits aren't made for trucks with a body lift, they are not high enough so mine had to be extended to get above the cab line. The kit required lots of cutting and notching and there were no instructions what so ever. The kit was I think $399 and the shipping was another $250 to have sent to KY. Check around at some of the offroad shops near you because most of the time they could probably build you a custom flat bed for cheaper.
Here are a few pics of mine, hope this helps out in your quest for a flat bed.