yes, you'll have to edit grub, since fedora has a history of not always finding other installs(however due to different HDD's, i think that's why it didn't detect.).
I think you'll probably be able to copy what's already in there for F8, except changing kernel versions and "f8" to "f7". If you mess up somewhere, just come back under F8 and post the grub for someone to help debug.
If you're not questioning my sanity, I'm not trying hard enough