Hello Tim,
I have found the John Bivins description from his old Rifle Magazine article to be extraordinary in its detail and anticipation of possible challenges. It is of the two piece construction, which for me has yielded better fit than the one piece construction. The modified files mentioned are of great assistance. If you call me during my workday, I can rummage around my file box and find the source on the files. They are course cut, non tapered, machine files. 541-858-2800