Aftermarket EGR's have a reducer washer that goes under the bottom of the EGR. The correct one is stamped with the number 11. In stock form, there is a reducer gasket on the end of the tube underneath the plenum. This helps to reduce a wide open throttle situation should the EGR tube break. Should that happen the engine will easily go over 3500 rpm. That could be a problem with an automamtic when coming to a stop.
Edited to add Bloozeberry's How-To EGR replacement. http://www.fiero.nl/forum/Forum9/HTML/000033.html
[This message has been edited by fierofool (edited 10-03-2014).]