Here's the a rear subframe from a 97-98.5 and a 98.5-04 sitting on top of it. The 97-98.5 has snap on tabs for adjusting the control arms while the 98.5-04 has them cast into the unit. The 98.5-04 rear subframe is also much more beafy and probably weighs a pond or two more than the earlier style. The spec guys break these more than anything and that's usually from side impacts.
The front subframe is also different and the easy way to tell the difference is where the control arm mounts. The early style is completely straight while the later style has a bow to it. The front subframe on the early cars doesn't show anymore likelihood to break than the later style.
