OK, I finally got it. My path name had a space in it, which in terminal is represented as a "\ " but in the script it did not need the backslash. I tried just copying ibRSBypass.dylib manually to the MacOS folder, but I guess the script does more than that. This is all with the very latest version of the game and v1.6 of the patch. I also have the "InCaseWeNeedIt" beta option enabled, if that has anything to do with it.
Now to try converting some Pavement to Mac versions!