Copy the shape of the .338 extractor seems to be the easy answer but take a close look at the bolt face and how far the extractor lays towards the center of the bolt face. Hold both bolts in your hands side by side.
If you get a round stuck in the chamber you can squeeze the side of the extractor and then it should snap over the rim of the 270.
James Wisner makes aftermarket M 70 extractors. He could help I am sure.
