I think as far back as '87 will bolt right up. If I'm not mistaken before that the few bed bolts that go in front of the right rear wheel went through the frame (the holes might still be there on the newer trucks?),whereas the 87-up has brackets on the outside of the frame rail to mount the bed in two spots.
I'd keep looking as well,I found this one a few years ago for my '87. It was sitting out behind a crane shop,they took it off a '93 when it was about a year old for a flatbed,and just had this one sitting. I got it for $100 and some elbow grease to clean the dirt off it from sitting so long,but it's like new. I even took the tailgate off and put it on evilbay and got my $$$ back.