Jason,
No extra screws left around?
That is strange, that a re-covering would change the CG that much. Did you recover with the same kind of covering, or did you do something different? I don't know about all coverings, but there is actually quite a differnece in weights between differnet colors of monokote. White is the heaviest, black is the lightest. But I'd never imagine 7oz of difference.

I suppose it's possible that you picked up a lot of oil soakage in the front of the plane, but 7oz of tail weight is huge.