In my opinion there is only one way that a barrel should be worked on and that is between centres when profiling, turning the barrel tenon and screwcutting and with a steady and head stock centre when chambering. This is why it is desirable to have a lathe with distance between centres of about 40" If you want to chamber in the headstock, which is the way lesser gunsmiths do it, then you dont need that kind of distance between centres.
This method is the only method that when set up properly gives the most accurate concentricity.
"Advanced re-barrelling of the sporting rifle" by Willis Fowler is an excellent book.
Fitting an indexed brake is a matter of simple maths.
Turn and screwcut your barrel as normal, fit the brake.
Align your barrel and using an engineers protractor, measure the angle of the muzzle brake
from the vertical, for example lets say 15 degrees out.
Again for example lets use a 20 TPI thread, this means that for each complete revolution of the brake it will move .050" on to the barrel. Divide .050" by 360 and this will give you linear movement/per degree which = .00014"for each degree of rotation. Multiply this by 15 and you have the amount of material to take off the shoulder and the corresponding amount off the muzzle to index the brake exactly which is .0021"