Surely any engine that fits in a 747 freighter also fits into an Anotnov 124/225?
They have certinaly flown 777 engines for AOG in the past.
And some large engines do also fit inside IL-76 aircraft, although I don't know if this includes 747/777 and A380 engines.
Can a 747-400 definitely pod a 5th engine as I've only ever seen Classics do it.