Hi,
I have found someone who installed successfully FCP 6 on Lion using Rosetta. Here are the information about that:
“Yes i have installed final cut 6.0.1 on lion on a new macbook pro. Lion did not want to play, so i bought a snow leopard disc and installed Rosseta ( found in the extras folder I think). This installed no problem on lion, and in turn rosseta enabled Lion to instal final cut 6. Works like a dream. So far no crashes and renders etc are all good.” Reference: https://roaringapps.com/forum-discussion:30
Good luck,
Maurice