The ST, Ex and Mounty share the same rear axle assembly. My wife's '97 V8 AWD Mounty has the shock on it, my '03 ST doesn't but has the mounting tab and holes for it. Since the accident last month, I had a whole new (10k miles on it) axle assembly installed on my ST. The axle assembly is from eithe a '99 or '01 Explorer, they swapped the ring and pinion (it had 3.73's, mine has 4.10"s), brake setup and sway bar.
In '01 they left some parts on from the Ex when they produced the ST, finally they caught on and removed it.