[outfield]

Here's an idea. Take the rear springs from a 67 and adapt them to the 99 frame. You won't be recreating the wheel this way, and the length should be okay. You may be able to reuse the 99 spring hangers, by just moving them. Or reuse the 67 hangers. Take dimensions from the doner truck so you know where the spring hangers should be placed. You could use 67 to probably 87 half ton springs. It would be worth investigating...