From the last post, Im assuming the rifle is "chambered" in .308, and isnt a 30-06 with the inserts.
Homerboys post sounded like it might be inserts, unless he was referring to the "block" that wont allow a clip of 30-06 to be inserted.
If it is the inserts, I think Id pass.
I have an M1 in .308 and its a shooter. I also have one in 30-06, and it too shoots well. I reload for both, so as long as I can get components, ammo cost really isnt an issue.
Other than the basic M1 safety issues (ammo and function) the only thing that I think you need to pay extra attention to, if you have guns in both calibers is, you dont get a clip of .308 into a 30-06 gun. To me, thats scarier than getting a 30-06 clip into a .308 gun. If you are shooting both at the same time, its very easy to get the clips mixed up, as they are really not all that different, unless held side by side.