You'll need a tubing micrometer to measure the neck thickness to determine how much it needs reduced to fit the chamber. Also if you're interested in accuracy it's best to turn the outside of the necks rather than ream them. A reamer just follows the hole that's already there, and if the necks are uneven they'll just be thinner and unever after reaming. Most neck reamers only come in stock sizes anyway, so ending up with the right neck OD could be pretty tricky.
The only Sako brass I ever had was very badly unconcentric, as bad as early LC 5.56 brass in fact.
