If I was putting it on a good original magnum length rifle, I'd get a new one from Duane Wiebe.

http://customgunandrifle.com/index.php?option=com_content&view=article&id=32&Itemid=48

Blackburn and Sunny Hill are also options, but actually taking delivery from either is (from what I've heard many times) very problematic. Duane is johnny on the spot and his metal work is superb.