A 767 isn't stealthy at all, and it isn't anywhere near as maneuverable as a fighter bomber. It would need lots of fighter cover to be able to fly over a target, and any high value target like a bunker used to process uranium into weapons grade uranium is going to have SAM's protecting it. I wonder if anyone has considered stretching an F-15 or other 4th generation fighter bomber to increase fuel and bomb loads?
Stealthy, definitely not. But Iran’s air defense is decrepit and fairly useless right now. A few cruise missiles, a few key air fields cratered, some electronic counter measures, a few grids knocked out and the door would be open. The real question is, would the bunker buster bomb currently available be up to the job. I don’t think the Iranians have the experience to harden their sites like we can in the West. Ultimately the best bet would be some sort of ground sabotage of key nuclear installations since it would allow the Israelis plausible deniability.