OK, status update time. Short and sweet, it's finished and I'm going to run cables instead.
The circuit works, barely. I guess for a 10mW transmitter I shouldn't expect too much. No matter how accurately I tune it, all I can get is a mono signal. The "stereo" indicator never lights on any receiver, and I've tried several. I can get good "tuned" indication, just not stereo.
Here are a couple pictures of the project and it's modifications.
This is the circuit. The blue 50K pot replaces two resisters and allows adjustment of the MPX Mix. Originally there were two 27K resisters in place.
The yellow wire going off to the left is a half wave length antenna.
Here is a picture of the entire circuit.
The small board with the two pots is both a 2.7 vdc. zener regulator and level adjustment circuit. (Thanks for the suggestion Al.)
As you can see, this can be powered by Micro USB +5 vdc. source.
All in all, it was good practice, but I am not satisfied with the result. So, either I drop a couple hundred $$ and by a better grade 25mW transmitter or I run cables. That is, unless someone here can tell me what the problem with this little beastie might be.