You could use either cargo coils (stiffer spring) or, if they'll fit the seats, a 3/4 ton spring. Not sure how much lift you'll get from that, though. Another option would be to add a spacer in the spring seat, which is how many of the lift kits for newer trucks works. You might also take a look at lift kits for the '73-'87 2wd trucks. I don't know if they're still being made or not, but they used to make them for 2wd desert trucks. Don't use the twist in stle spacers, those are meant only as a temporary fix for a sagging spring, not a permanent lift. Those can cause severe stress on the spring, leading to failure.
One more thing to keep in mind, especially on the front, depending on how high you go, you can put things to the point that it cannot be properly aligned.
