BSteele,
You might check with Lothar Walther, I just looked on their site and they have a full octagon barrel with rib. While the illustrations show it for a Mauser, I gather they will make it for whatever you want. I don't know if they will round the muzzle portion now if they have the proper diameter bore. But WTH a phone call should settle that. By the time you buy an acceptable barrel, rebore it, sleeve the breach to fit an 03 you might be $ ahead to get one of theirs.

Thaine

It ain't ignorance that does the most damage, it's knowing so derned much that ain't so! J. Billings