Give Ohio Ordnance Works a call....they list them in their ads.......and years ago, Bob use to sell conversion kit to convert from 8x57mm to 7.62x51mmNATO/.308.
Heck buy an inexpensive barrel blank and take it to a gunsmith along with a beater barrel set up. I bet your talking to contour and thread the barrel about 150 - 200 plus the barrel
Hard to find a blank that is large enough in the rear. I have been looking to do that. Brownells didn't have anything. Any other large sources for barrels?
At one time I considered converting my 34 to .308 and searched for the necessary conversion parts. At some point in time this may be a something to have, but right now, with the abundance of cheap, QUALITY 8mm, I see no reason to convert to .308 unless you just don't like shooting corrosive ammo.