It looks like the only outside GNOME for Slackware that's
actively maintained is this one:
Since it replaces some system components, using it voids your
warranty. But it should work, *if* you absolutely must have
GNOME. I'd suggest XFce instead if you want a GTK+ based desktop.
If you do want to use Dropline, they may be updating a few things
after 12.0 releases, so it might be best not to rush into it.
Need more build scripts? Something that you wanted wasn't
included in Slackware? Well, then check out slackbuilds.org.
Several of the team members work on the scripts there.
Che non conosca GSlacky lo capisco! Ma almeno una citazione per Slacky!