Your best bet is to go back to your Snow Leopard volume and the old iPhoto file to complete your project.
The iPhoto Library has changed a number of times over various releases; the latest iteration is a unified library that both iPhoto and Aperture can share. I have no reason to believe FCE will ever be able to use either the package library or the unified library. FCE was discontinued over 18 months ago, so no updates and certainly no new features/capabilities.
An alternative may be to export all the images that you used in the FCE project from your iPhoto 8.1.2 Library to a folder on your hard drive; then try reconnecting media to the exported images.