Varminter, this one is a true no brainer, you don't even have to disasemble the ejector, just use a small clamp to hold it closed, that is how I did my 357 rechamber. The chamber diameter doesn't change, only the length of the chamber. The reamer will center itself in the exisitng chamber, it doesn't even require a lot of force, in fact force is exactly what you don't want. A local gunsmith should be more than capable of doing this for you, the reamer can be rented at
www.reamerrentals.com It is a 10 minute job, the reamer should arrive at the gunsmith, he should call you, you show up with barrel in hand, in 10 minutes or less you walk out with a 445 Super Mag barrel. Do be aware, the 445 is a reloading only proposition. You can buy new brass from any catalog supplier that carries Starline Brass,
www.midwayusa.com comes immediately to mind. I can't think of a more user friendly cartridge for a beginning reloader to start on, other than a 44 Mag or 357 Mag or 38 Special