Before I offend our 1st Gen pals, there were some D350 SRWs.
As far as 2nd Gens, 2500s with the camper package will have the overload springs and rear swaybar, so the springs will look like those from a 3500.
It sounds to me like someone has:
1. Put a 3500 cab on a 2500 frame (no diff between a 1500, 2500 or 3500 cab - just the door jamb stickers, VIN tag and emblems on the doors)
or
2. Put a SRW bed(1500 or 2500) and single wheels on a 3500.
Good luck.
Mike