[gembud] Installing GEMPAK on Mac OS X Mountain Lion (10.8)

I'm using the following instructions to build GEMPAK for Mac OS X: 
https://www.unidata.ucar.edu/software/gempak/doc/install_osx.html

I am getting an error building OpenMotif 2.3.3 (Step 3c):

make  all-am
/bin/sh ../../libtool --tag=CC   --mode=compile gcc -DHAVE_CONFIG_H -I. 
-I../../include -I.. -I./.. 
-DXMBINDDIR_FALLBACK=\"/opt/local/lib/X11/bindings\" 
-DINCDIR=\"/opt/local/include/X11\" -DLIBDIR=\"/opt/local/lib/X11\"     
-I/opt/local/include -Wall -g -fno-strict-aliasing -Wno-unused -Wno-comment 
-fno-tree-ter -I/opt/local/include -I/opt/local/include/freetype2   -MT 
XmStrDefs.lo -MD -MP -MF .deps/XmStrDefs.Tpo -c -o XmStrDefs.lo XmStrDefs.c
libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I../../include -I.. -I./.. 
-DXMBINDDIR_FALLBACK=\"/opt/local/lib/X11/bindings\" 
-DINCDIR=\"/opt/local/include/X11\" -DLIBDIR=\"/opt/local/lib/X11\" 
-I/opt/local/include -Wall -g -fno-strict-aliasing -Wno-unused -Wno-comment 
-fno-tree-ter -I/opt/local/include -I/opt/local/include/freetype2 -MT 
XmStrDefs.lo -MD -MP -MF .deps/XmStrDefs.Tpo -c XmStrDefs.c  -fno-common -DPIC 
-o .libs/XmStrDefs.o
In file included from XmStrDefs.c:10:0:
../Xm/Xm.h:81:27: fatal error: X11/Intrinsic.h: No such file or directory
compilation terminated.
make[3]: *** [XmStrDefs.lo] Error 1
make[2]: *** [all] Error 2
make[1]: *** [all-recursive] Error 1
make: *** [all-recursive] Error 1

Any ideas on how to get around this?

Thanks,
Seth