I seem to recall that there was an insert that was placed into the chamber of the M1 so that it could shoot the 7.62N. I do not recall if this insert was also used on the 03. I also seem to recall that it didn't always work. If memory serves, the Navy used this insert and there were some on the market years ago. Another option is to have the barrel recut. To get the 308 chamber will result in a shorter barrel. The other option is to buy a new barrel and have it chambered for the 7.62N. A good smith will keep the shape the same as the stock barrel. The one thing that I have no info on is how the rounds will feed from the mag, since it is a bit long for the 7.62. Just thinking out loud, but it would seem that the feeding could be a bit troublesome.
Good Luck, SSC