As per this question, the 'run' command uses the wrong interpreter regardless of the configuration settings for the run action, and it appears the only way to fix it is to directly edit the source of pydev itself:
Even after importing the python2.7-32 interpreter as the ONLY defined one, the output of the 'See resulting command-line for the given parameters' on OSX reads:
The PYTHONPATH that will be used is:
When the configured path to the interpreter is:
This appears to be because the run command is using the sys.executable value INSTEAD of the value that is configured with the selected interpreter, which is the heart of this bug.