Tonight I wrote an RSS 1.0 type-file for Thistle; you can
<a href="http://www.scotlandsoftware.com/blog/dev/thistle/thistle_rss10_type.tgz">download it here</a>.
It includes support for the same <code>excerpts</code> parameter as the RSS 2.0 type included with Thistle, so
your feeds can contain either excerpts or full posts.
It will work fine with the current version of Thistle (0.2/0.3), and when the next version is released
it will automatically gain new features (including contextual titles and the RSS 1.0 <code><items>...</items></code>
You can see an example of the full functionality by looking at my Thistle category's
<a href="http://www.scotlandsoftware.com/blog/?cat=/dev/thistle&type=rss1&excerpts=1">RSS 1.0 (excerpts) feed</a>,
and you can validate your feeds at the <a href="http://www.w3.org/RDF/Validator/">W3C RDF Validation Service</a>.