OK, I got it to install OK, now just need to figure out how to use it.
I tried to use a logo image, but the image picker page doesn't allow me to save or cancel. I have to use my browser's back button to return to the Template Manager: Edit Style page.
Another thing I noticed is that in the gk_creativity_rest_files_J!3 package, the plugin plg_gkcontact fails to install. It looks like its XMS uses <install ... /install> rather than <extension ... /extension>