to use the region free ability of your chip you need to downgrade to 4.1 (4.2/4.3 kill it)
here is a guide for that.
to your current issues with the loader you can check out the FAQ on the softmod basics linked below.
Black and white or green screen indicate wrong setting of your videomode. try: force ntsc.
don't know anything about the GC stuff.
good luck for now