To update this problem:

I had a look at the Apache config file - no apparent aliasing problems there.

What was incorrect, in the swish.cgi-generated form, was that the line that starts:

 <form method="get" action="/swish.cgi" 

needed to be changed to  <form method="get" action="/cgi-bin/swish.cgi

This was because the Apache config had been set  to assume that the alias 
/www/htdocs was the (user) root.

So, when the form referenced /swish.cgi, it was sent to /www/htdocs/swish.cgi - wrong 
place.

Sending the request to /cgi-bin/swish.cgi results in the request going to /www/cgi-
bin/swish.cgi, which is correct. I am not completely clear on this, but it works.

Related question:

It appears that the TemplateDefault.pm module is run from

/usr/local/lib/swish-e/perl/SWISH/

rather than from the install directory, /usr/local/lib/swish-e/perl/

Is this in the docs for the script? I figured it out by finding all of the instances of 
TemplateDefault.pm on the server, and changing the hex codes on one of the table rows 
to different values on each instance, then observing the output results.

Thanks again for your patience and help!

--- Phil Matt