how to make External.php to show only titles from specific forums. (simple RSS)

[Lynne]

I have not seen many people wanting to completely delete their outgoing topic text - what is the purpose of having your RSS feed on if you do that?

As for what to do... go through the file and anything the message is set, set it to nothing. For example, line 715 (picked at random), it says:
$message = $postbit_obj->construct_postbit($thread);

So, set that to:
$message = '';

Of course, if you can read the code well enough, you can follow that line up, or down, and see if you need to change anything else within that bracketed code.

another example around line 737 is:
$xml->add_tag('description', $plainmessage);

change to:
$xml->add_tag('description', '');