I doubt an F-15 could carry a 30,000+ bunker busting bomb - the limit is about 23,000 of external fuel/ordinance. I’m thinking a converted 767 could carry several. It would be a difficult re engineering project of the plane but not impossible.
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?