I just double checked, MGW does have the barrels in stock. When you search you will find them under the lighting/lightweight BLR's. All takedowns are lightwieghts, or aluminum framed. The 81 tab will just give the threaded barrels. Good luck with the headspace, I am beginning to think that...
You can buy takedown barrels from gunparts corp and Midwest gun works. I bought two and both headspaced on my Blr. After a rebore I have a 338 win mag and a 375 wildcat is with Jesse for a reborn in Oregon.