With the 6.4.0 release, we replaced the old "Like Box" widget with the new "Pages Plugin". The Like Box is what used to display the Facebook Fan Page information, but Facebook announced that they were removing that module and it should be replaced with the Pages plugin.. so we did that. The old Like Box widget will no longer work at the end of June, so we wanted to make the switch now before the widget wouldn't show at all.
Unfortunately, the new Pages Plugin displays a little differently than the older Like Box plugin and also has some different restrictions. Specifically, the width can only be be between 280 and 500px. There's no way to go larger, or smaller, than that. For all the settings and options of the new Pages Plugin, please see Facebook's documentation:
developers.facebook.com/docs/plugins/page-plugin
I hope that helps explain, even if it's not what you were looking to hear.
Thanks,
Alex