The 4x4 shocks are thicker and won't fit the 2wd hubs. An other option would be is that they are standard (non Cosworth) Sierra struts. But that also seems unlikely as those are actually longer than 2wd Cosworth struts.

You don't have the old Motorcraft shocks anymore to compare with the Bilsteins?
You also shouldn't have them bottoming on new shocks on small bumps. Perhaps the shocks are not even for a Sierra but for a completely different car (that is lighther as well). Perhaps you can check the Bilstein part number to see if they are the correct part.