If you can make a simple tube frame, you can get just about any buckets to work. I got some seats out of a '93 Firebird wreck and made me a tube frame with 1X1 square tube and some 1/8" steel plate and mounted them up using the back hole of the bench seat mounting location because it would line up with the tabs on the Firebird seats. They're more comfortable in the truck than they were in the 'bird!
If you like the big 'ol seats out of the later Subs, you can make them work, but I doubt there are any other seats that will bolt right up, except maybe some of the buckets that came in a vert few of the pickups, starting in about '85 and going to '87, I think. I would think those seats would come pretty close to matching up, but they're probably hard to find.