Down through the years there has been an ongoing debate about the interchangeability of .223 and 5.56. We will leave that for another time.
But, I have often wondered about whether the .308 and 7.62X51 is interchangeable. So, I did some research. Here is one link that tries to sum it up:
Fulton Armory: What's the Difference between .308 Winchester & 7.62x51mm NATO?