Here is a good write up:
http://www.westernshooter.com/2009/1...age-rifle.html

The best index mark I had in a barrel was when I used the long screw in the front base. It distorted the threads enough that it works great. If I look thru that hole I can clearly see it.
Speedy, I dont know what type vise you are using but if you can use a separate vise on the action and the barrel (clamping the barrel in wood) you can do the replacement without moving the barrel.
Either way, double check with the gauges for piece of mind.