Thanks for the suggestions!  

I rebuilt both gr-osmosdr and rtl-sdr from scratch, with the addition of changing the install directory to /opt/local in the cmake_install script.  I also ensured that all parts of the old installs in /usr/local were deleted.  

Steps:

1) go to the build directory of both packages and do a "rm -rf *" to ensure -everything- is cleaned out;

2) cmake ../

3) vi cmake_install script and change /usr/local to /opt/local at the top.

4) make

5) sudo make install

This put everything in the correct place, but still a no-go.  Python chokes on the line in top_block.py that says "import osmosdr".  Module not found.

I tried PYTHONPATH again to see if I could give python a hint, but no go.  

Just seems that python needs to be able to find the osmosdr module.  

Marcello, thanks for the suggestion re the build-gnuradio script, but it won't work on a Mac/Darwin.  It took the better part of a month working with the macports.org folks just to get gnuradio to compile cleanly and run.  It's a very complex port for them, with everything (just about) going into different places, so I wouldn't want to even risk trying it.  Might screw my main machine up!

If I can't get this running I may just go back to an Ubuntu machine for gnuradio.  The Mac would be better for my needs though, as I travel a bit and want to use grc etc on the road.  That was the impetus for getting the package to run on the Mac in the first place.

Kevin