Sean,
Everything you mention above *should* make the SCLogin module show the Twitter button. My best guess as to what's wrong is that you installed JFBConnect and then installed JLinked. JLinked has an older version of the SCLogin module, and that would have downgraded your version.
If you could, go to your Install Manager area and go to the Update section. From there, hit the "Find Updates" button and see if an update for the SCLogin appears. If so, install it, and hopefully you'll be fixed right up.
If not, let us know, and we'll gladly help more.
Thanks,
Alex