Q: How do I access a project from iPhoto library?

Use iPhoto to finish these projects in iPhoto.

Photos is using different book themes and book sizes from iPhoto, so books and calendars do not migrate well to Photos, see this support page:

How Photos handles content and metadata from iPhoto and Aperture - Apple Support

• Some photo books and calendars, made with themes that are no longer supported in Photos, migrate to Albums.

Do you have iPhoto 9.6.1 installed? Then you can directly open your iPhoto Library in iPhoto.

• If you already have this version installed, drag it back from the Applications folder to the Dock and launch it.
• If you still need to install the update, you can only update by reinstalling from your Purchases history at the App Store.

Barney-15E's user tip explains how to update to iPhoto 9.6.1 by reinstalling your App Store purchase.

See this link:   Get iPhoto 9.6.1 if you didn't update before OS X 10.10.3

Basically, move the incompatible iPhoto version from the Applications folder  to the Trash (the application, not your iPhoto Library). Then sign into the AppStore and open the purchases tab. It should now show "Install" to the right of iPhoto.

but I get "This item is temporarily unavailable.  Try again later."  Have you seen this before?

You have been trying to reinstall from your Purchases History, right?  I have not seen it for iPhoto, but for GarageBand '11, another iLife '11 application, that is uno longer supported by Apple. It keeps coming and vanishing again from the AppStore  like the Cheshire Cat, whenever there are major maintenance works going on at the AppStore. Keep trying to install.

Don't empty the Trash with your older version, until you could update.

I just tested again. iPhoto is downloading and installing just fine, when I am going to the App Store.