If you have installed both the LispWorks images, for native Mac OS X and for GTK+, you will want to configure two images.
If necessary your Lisp configuration and initialization files can run code for one image or the other by conditionalization on the feature :cocoa. The native Mac OS X LispWorks image has :cocoa on
while the GTK+ LispWorks image does not, and has
LispWorks Release Notes and Installation Guide - 23 Dec 2011