Were you going to bag it or keep it stock? Because if so, there are entire 4/5 link backhalfs you can get for bagged applications (Thor Bros. etc.)

If you have coin to spend on this project, this guy can bend up custom frame rails or you could try adapting his S10 frame to the Mighty Max (they're close to each other in design).

http://autoweldchassis.com/frames.ivnu

If you're keeping it stock, it might be worthwhile to not throw good money after bad and start over with another truck, or at least one with a salvageable frame. They're not too tough to find.