I bought my own die, centering guide and handle from FAC a few years ago, and I did the barrel on my SA-85M to put on a slant brake. I was not about to remove the sight base on this beautiful rifle to make it a total correct job. I threaded until the die hit the sight base, then I turned the die around which got me right up to the base. I threaded on the brake, used some clear epoxy on the threads and indexed it with the hole in the base. I have a small gap between the brake and the sight base, but it's not something that jumps out at you. Plus, I can always go back and take the base off and do it right if I want. I could have also used a peel washer between the brake and the sight base, then gone back and darkened the peel washer with a Sharpie.
Whatever you do, you will need the centering guide, which is just a .30 caliber stub for the barrel with a threaded head so the die rides it onto the barrel, giving a straight start.