^^ What he said, however I'm guessing that he intended to put a "not" in the phrase "I certainly would (not) go to the expense..."
"Differences" in fact, not specification, are an internet myth. Pure and simple. The differences on the barrel is the stamp. Go to Brownells and see if you can find a different chamber reamer for .223 and 5.56MM.
They are the *same*..... any gunsmith that you brought this to to rebarrel and rechamber from .223 to 5.56 would laugh at you... unless he kept quiet and laughed all the way to the bank.